Add Crashlytics for error tracking (optional).

To use the error tracking, you need to add a Crashlytics API key to the
AndroidManifest.xml of the enabler.

See #111.
Fix Eclipse build for enabler.
Merge branch 'next' into crashlytics
Add bogus Crashlytics API key to allow build.
Add Crashlytics JAR for Eclipse build.
Fix Travis CI build by adding build-tools from Android SDK.

Fixed #55 - finally!
Fix Travis CI build by adding build-tools from Android SDK.

Fixed #55 - finally!
Only run tests suite for openxc-it on CI.
Merge branch 'ci-fix' into next

Conflicts:
	.travis.yml