Add support for user defined Actions
Add support for user defined Actions

It may be useful for users to be able to return their own custom
Action types in the Config callbacks. For a contrived example, a user
could add a jar file in the .ivy2 directory to the watch sources and
trigger a reboot full when that jar changes.

mdedetrich/sbt,mdedetrich/sbt,mdedetrich/sbt,sbt/sbt,sbt/sbt,mdedetrich/sbt,xuwei-k/xsbt,xuwei-k/xsbt,xuwei-k/xsbt,sbt/sbt,sbt/sbt,mdedetrich/sbt,mdedetrich/sbt,sbt/sbt,sbt/sbt,xuwei-k/xsbt,sbt/sbt,xuwei-k/xsbt,mdedetrich/sbt