Stability fixes

* Fixed a deadlock caused by the mutex staying locked when the menu (or other blocking operation) is triggered during the playloop, and freezing the app when going out to save the instance state. Now it only is locked during map state operations.
* Fixed the main activity to be single-task, hoping to eliminate the bug on my old Android phone where the start screen would appear despite there being an instance state saved
* Now Quit calls exit() on Android, throws exceptions elsewhere. Apparently Android NDK just crashes with signal 11 on exceptions :|, making exception handling not portable
Named the door constants.
Undid the manifest activity change. It didn't work as expected. Instead I added something onCreate MainActivity, hoping that it works.