Improve overall exception handling and error feedback to the user

The main goals of this patch are to:
- Improve the exception handling in Aegis and the way we present errors messages
  to the user when they occur.
- Write exception stack traces to the log in more places, so that the ADB logs
  we ask for from our users when reporting bugs become more useful.
- Reduce the amount of times we throw a RuntimeException, particularly when an
  Android Keystore operation fails.

Achieving the above goals ended up resulting in a very large refactor. The
intro and unlock flow of the app need to be retested entirely.

app/src/main/res/layout/dialog_error.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    android:orientation="vertical"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:paddingStart="25dp"
+    android:paddingBottom="10dp"
+    android:paddingEnd="25dp"
+    android:paddingTop="10dp">
+    <TextView
+        android:id="@+id/error_message"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"/>
+    <TextView
+        android:id="@+id/error_details"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:visibility="gone"
+        android:layout_marginTop="10dp"
+        android:textStyle="italic"/>
+</LinearLayout>