Introduce UUIDMap for storing objects that are keyed by a UUID

This patch introduces the new ``UUIDMap`` type, reducing code duplication and
making UUID lookups faster. We currently already use UUIDs as the identifier for
the ``DatabaseEntry`` and ``Slot`` types, but the way lookups by UUID work are
kind of ugly, as we simply iterate over the list until we find a match. As we're
probably going to have more types like this soon (groups and icons, for
example), I figured it'd be good to abstract this away into a separate type and
make it a map instead of a list.

The only thing that has gotten slower is the ``swap`` method. The internal
``LinkedHashMap`` retains insertion order with a linked list, but does not know
about the position of the values, so we basically have to copy the entire map to
simply swap two values. I don't think it's too big of a deal, because swap
operations still take less than a millisecond even with large vaults, but
suggestions for improving this are welcome.

I had to update gradle and JUnit to be able to use the new ``assertThrows``
assertion method, so this patch includes that as well.

app/src/test/java/com/beemdevelopment/aegis/HOTPTest.java

@@ -3,12 +3,12 @@ package com.beemdevelopment.aegis;
 import com.beemdevelopment.aegis.crypto.otp.HOTP;
 import com.beemdevelopment.aegis.crypto.otp.OTP;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
 
-import static org.junit.Assert.*;
+import static org.junit.jupiter.api.Assertions.*;
 
 public class HOTPTest {
     // https://tools.ietf.org/html/rfc4226#page-32

app/src/test/java/com/beemdevelopment/aegis/SCryptTest.java

@@ -5,13 +5,13 @@ import com.beemdevelopment.aegis.crypto.SCryptParameters;
 import com.beemdevelopment.aegis.encoding.Hex;
 import com.beemdevelopment.aegis.encoding.HexException;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.util.Arrays;
 
 import javax.crypto.SecretKey;
 
-import static org.junit.Assert.*;
+import static org.junit.jupiter.api.Assertions.*;
 
 public class SCryptTest {
     @Test

app/src/test/java/com/beemdevelopment/aegis/TOTPTest.java

@@ -4,12 +4,12 @@ import com.beemdevelopment.aegis.crypto.otp.OTP;
 import com.beemdevelopment.aegis.crypto.otp.TOTP;
 import com.beemdevelopment.aegis.encoding.HexException;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
 
-import static org.junit.Assert.*;
+import static org.junit.jupiter.api.Assertions.*;
 
 public class TOTPTest {
     private static class Vector {

app/src/test/java/com/beemdevelopment/aegis/UUIDMapTest.java

@@ -0,0 +1,104 @@
+package com.beemdevelopment.aegis;
+
+import com.beemdevelopment.aegis.util.Cloner;
+import com.beemdevelopment.aegis.util.UUIDMap;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeEach;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class UUIDMapTest {
+    private UUIDMap<Value> _map;
+
+    @BeforeEach
+    public void init() {
+        _map = new UUIDMap<>();
+    }
+
+    @Test
+    public void addValue() {
+        // try adding a new value
+        Value value = addNewValue();
+
+        // try re-adding the value
+        assertThrows(AssertionError.class, () -> _map.add(value));
+
+        // try adding a clone of the value
+        assertThrows(AssertionError.class, () -> _map.add(Cloner.clone(value)));
+    }
+
+    @Test
+    public void removeValue() {
+        // try removing a value
+        final Value value = addNewValue();
+        Value oldValue = _map.remove(value);
+        assertFalse(_map.has(value));
+
+        // ensure we got the original value back
+        assertEquals(value, oldValue);
+
+        // try removing a non-existent value
+        assertThrows(AssertionError.class, () -> _map.remove(value));
+
+        // try removing a value using a clone
+        Value value2 = addNewValue();
+        _map.remove(Cloner.clone(value2));
+        assertFalse(_map.has(value2));
+    }
+
+    @Test
+    public void replaceValue() {
+        Value value = addNewValue();
+
+        // replace the value with a clone
+        Value valueClone = Cloner.clone(value);
+        Value oldValue = _map.replace(valueClone);
+
+        // ensure we got the original value back
+        assertEquals(value, oldValue);
+
+        // ensure that the clone is now stored in the map
+        assertSame(_map.getByUUID(value.getUUID()), valueClone);
+    }
+
+    @Test
+    public void swapValue() {
+        Collection<Value> values = _map.getValues();
+
+        // set up the map with some values
+        Value value1 = addNewValue();
+        Value value2 = addNewValue();
+        Value value3 = addNewValue();
+        Value value4 = addNewValue();
+
+        // set up a reference list with the reverse order
+        List<Value> ref = new ArrayList<>(values);
+        Collections.reverse(ref);
+
+        // the lists should not be equal at this point
+        assertNotEquals(values, ref);
+
+        // swap the values and see if the lists are equal now
+        _map.swap(value1, value4);
+        _map.swap(value2, value3);
+        assertIterableEquals(values, ref);
+    }
+
+    private Value addNewValue() {
+        Value value = new Value();
+        assertFalse(_map.has(value));
+        _map.add(value);
+        assertTrue(_map.has(value));
+        return value;
+    }
+
+    private static class Value extends UUIDMap.Value {
+
+    }
+}