Install an uncaught exception handler in Aphlict

Summary:
Ref T5373. This seems to work pretty much correctly.

Also stop popping bubbles and just use the log, since users find the bubbles confusing/not useful and they're not great for developers either.

Future diffs will expose more user-facing stuff.

Test Plan: Added `throw` to AphlictClient.as, got a log in the parent window.

Reviewers: joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T5373

Differential Revision: https://secure.phabricator.com/D9698