Unset "singleTask" as the launchMode for MainActivity

We don't actually need this, and I have a feeling that it may be causing some of
the inexplicable crashes we're seeing in the Play Console. For example:
apparently the app sometimes gets itself into a state where the vault is
unlocked, but the user is still shown AuthActivity (possibly due to it being
launched twice). I can't prove that "singleTask" causes this, as I can't
reproduce the issue on my device or an emulator, but it's the only odd thing we
have in our activity lifecycle handling.

Test plan:
- Go through the intro, add an entry, change some settings, etc
- See if the app shortcuts still work. Scenarios:
    - The app is terminated.
    - The app is locked.
    - MainActivity is open.
    - Some other activity is open.
- See if auto-locking still works. Scenarios:
    - The app is locked.
    - MainActivity is open.
    - Some other activity is open.
- Turn on "Don't keep activities" in developer options and repeat the above
  steps.

app/src/main/java/com/beemdevelopment/aegis/ui/AegisActivity.java

@@ -35,7 +35,7 @@ public abstract class AegisActivity extends AppCompatActivity implements AegisAp
         // if the app was killed, relaunch MainActivity and close everything else
         if (savedInstanceState != null && isOrphan()) {
             Intent intent = new Intent(this, MainActivity.class);
-            intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
+            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
             startActivity(intent);
             return;
         }