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/java/com/beemdevelopment/aegis/ui/ScannerActivity.java

@@ -107,7 +107,6 @@ public class ScannerActivity extends AegisActivity implements ZXingScannerView.R
     @Override
     public void handleResult(Result rawResult) {
         try {
-            // parse google auth uri
             GoogleAuthInfo info = GoogleAuthInfo.parseUri(rawResult.getText().trim());
             VaultEntry entry = new VaultEntry(info);
 
@@ -116,10 +115,11 @@ public class ScannerActivity extends AegisActivity implements ZXingScannerView.R
             setResult(RESULT_OK, intent);
             finish();
         } catch (GoogleAuthInfoException e) {
-            Toast.makeText(this, getString(R.string.read_qr_error), Toast.LENGTH_SHORT).show();
+            e.printStackTrace();
+            Dialogs.showErrorDialog(this, R.string.read_qr_error, e, (dialog, which) -> {
+                _scannerView.resumeCameraPreview(this);
+            });
         }
-
-        _scannerView.resumeCameraPreview(this);
     }
 
     private void updateCameraIcon() {