Dependencies upgrade

- Upgraded build system to SBT 0.13.0 ( plugins upgrades to their latest versions)
- Upgraded Scala to 2.10.2
- Upgraded to Akka 2.2.0 and Play Iteratees 2.2.0-RC1
- CustomEnumeratee and TakeTo now take implicit ExecutionContext (as needed by Play Iteratees 2.2)