Release/scala ide 3.0.x to 2.11 and beyond

Based on the initial work by @huitseeker, this PR brings 2.11 builds to the stable branch (3.0.x).

* many commits were backported, some were manually re-enacted due to way too many conflicts
* bumped version to 3.0.4
* moved to the OSGi bundles, which means plugins for 3.0.4 will need to update their dependencies
* last few commits might be interesting to forward-port to master

I built locally with both 2.10 and 2.11, and all tests pass.