Made ScalatraBroadcaster into a trait for custom broadcasters. Moved some logic into a DefaultScalatraBroadcaster that gets used by default. Additionally made a RedisScalatraBroadcaster that uses the atmosphere-redis plugin. Custom broadcasters can be used by changing the new scalatraBroadcasterClass member in the AtmosphereSupport trait.
Merge pull request #300 from jgrowl/2.3.x_2.10

atmosphere-redis plugin support and moved ScalatraBroadcaster into a trait