Support for group inserts of entities.

Hey, Forger!
iNeed(16).of(RamGigabyte.class).in(myMacbook); // otherwise I'll go nuts with Gradle + Android Studio!

This pull-request is rather a snapshot. Just wanted to let you see in which direction I'm going.

TODO:
- Make MultiInsertor work faster. For bigger amounts of data it'll suck to query for every single row just after insert (and that's how it's done now). What I'll do probably is applyBatch(model.getUri().getAuthority(), ArrayList) and then query() with "WHERE IN (joined data from ContentProviderResult[])". However, I need to extend EchoContentResolver by mocked applyBatch first.
- Change "GroupFakingTest" name to something more appropriate.