Show a popup if the main thread panics

[tomaka]

The app freezing or showing a black screen is not very useful and does not indicate what's wrong.

This should probably be done by overriding the default panic handler instead of using catch_panic, so that the user can override this behavior if wanted.

[tomaka]

Unfortunately since we're calling start manually, there's no way to either override the panic handler or to use catch_panic.

In my opinion the best thing to do is try detect the words thread <main> panicked in stderr, and open a popup when it happens.

[tomaka]

Reference: https://developer.android.com/guide/topics/ui/dialogs.html#AlertDialog