Implement a default uncaught exception handler

[ewpatton]

Change-Id: Icb5517fad7968978e2a21a4de6078d1407308829

General items:

• [ ] I have updated the relevant documentation files under docs/
• [x] My code follows the:
  • [x] Google Java style guide (for .java files)
  • [ ] Google JavaScript style guide (for .js files)
• [x] ant tests passes on my machine

If your code changes how something works on the device (i.e., it affects the companion):

• [x] I branched from ucr
• [x] My pull request has ucr as the base

Further, if you've changed the blocks language or another user-facing designer/blocks API (added a SimpleProperty, etc.):

• [ ] I have updated the corresponding version number in YaVersion.java
• [ ] I have updated the corresponding upgrader in YoungAndroidFormUpgrader.java (components only)
• [ ] I have updated the corresponding entries in versioning.js

For all other changes:

• [ ] I branched from master
• [ ] My pull request has master as the base

What does this PR accomplish?

Description

Fixes #3179 by setting a custom handler for when threads throw uncaught exceptions. Note that the behavior is different between Form and ReplForm, where the latter reports errors back to the editor via RetValManager.

[ewpatton]

@jisqyv Here is a test app with an extension that just throws an error on another thread using AsynchUtil.

ExceptionTester.aia.zip