Refactor dark mode to allow multiple themes

app/src/main/java/com/beemdevelopment/aegis/Theme.java

@@ -0,0 +1,19 @@
+package com.beemdevelopment.aegis;
+
+public enum Theme {
+    LIGHT,
+    DARK,
+    AMOLED;
+
+    public static Theme fromInteger(int x) {
+        switch(x) {
+            case 0:
+                return LIGHT;
+            case 1:
+                return DARK;
+            case 2:
+                return AMOLED;
+        }
+        return null;
+    }
+}