safer sessions, got rid of threadLocalSession
piggybacks slick session onto play request, reducing boilerplate

* renames SlickAction to DBAction (looks more seamless this way and future play users will know what DB means, but may be confused what Slick is)
* DBAction now passes a RequestWithDbSession which combines a Play Request and a Slick Session to its argument. Two implicit conversions implicitly convert it to either of the two. This way DBAction automatically provides an implicit Session, removing the need for calling withSession explicitly every time. DBAction uses withSession internally, which provides a session object, but opens/fetches a connection lazily only on first use. The session is closed by DBAction when the request ends. To tune performance, users can close the session early at any time using its close() method. Also, users can still use withSession themselves if they want open and close sessions multiple times. This change does not only reduce boilerplate, but also makes it more transparent where databases accesses happen, because it requires a DBAction instead of an Action (unless withSession is used explicitly, which should be need rarely).
replaces play-slick's custom DB interface by Slicks standard one

* refactored play-slick DB/Config classes into Database. This means minor simplifications with API and imports.
* removed play-slick custom DB interface and inherited from scala.slick.session.Database instead. This makes slick-play apps compatible with ordinary Slick, which would for example allow shared code between a slick-play app and a pure slick app.
* moved DBAction out of the cake using AsyncResult instead of Async. This makes it more universal and it just comes with the import, not need to inherit a slice. Be aware, that AsyncResult and Async will both be deprecated in the next play version in favor of Action.async (at least that's what current master says).
* minor refactorings of slick-play
Merge branch 'topic/closerToSlick' into scaladays2013

Conflicts:
	samples/computer-database/app/Global.scala
	samples/computer-database/app/controllers/Application.scala
	samples/computer-database/app/models/Models.scala
named untyped ids more explicitly
renamed typed id fields to id
condensed query library boiler plate
condensed id type mappers into single implicit