Robolectric 2.3 support without any Robolectric modifications

This branch pulls up all the private logic from RobolectricTestRunner into BurstRobolectricRunner.  Unfortunately, it's only compatible with Robolectric 2.3 right now, but with some minor changes to Robolectric (next major version) we could easily remove most of the logic from BurstRobolectricRunner.
This won't work because no plugin is providing the 'apk' type, but the dependency itself isn't needed.