Move StreamPlugin to a dedicated package

XD-142 Fix early instantiation of beans in module context

- Remove StreamPlugin usage of Module.getComponents
causing bean instantiation before module start

- Add hook for Plugins to add shared bean definitions
to the common context

- Add post processors for modules to register their
own channels with the ChannelRegistry

- Add context destroy to Module stop, as context
cannot be re-refreshed on start anyway

XD-142 Add stream deploy integration test

on merge: changed source index to 0 in test

on merge: removed trailing whitespace