Refs #82 - Add Mysqli/NestedTransactionConnection and an Adapter that returns it.
Refs #82 - Update DbServiceProvider to use our adapter subclass.
Refs #82 - Add getDbAdapter method to AbstractMapper.
Refs #82 - Fix path to Mysqli driver.
Merge pull request #82 from synapsestudios/feature/82-nested-transactions

Add support for simulated nested transactions