Reactive Mongo Initial Commit

- Cleaned up casbah readme.
- Setup reactive mongo journal.
- Modifed Build.scala to support reactive mongo IT tests.

Pull request modifications from comments

- Updated readme.md to reflect reactive mongo.
- Modified Reactive Journal to manage mongo connection.
- Modified Reactive Journal Properties to accect mongo connection
configuration variables.
- Updated test fixtures and support specs to support journal's
management of mongo connection.
- #83 ReactiveMongo Journal

Address unique index sequence number for reactive mongo

- Updated ReliableChannelSpec to set sequenceNr.
- Updated MongodbReactiveJournal to use insert to return future.
- #83 ReactiveMongo Journal