Use plain Scala OSGi bundles to build the IDE.

* toolchain is used only to build sbt
* all Scala-related dependencies are resolved through Maven
* bundles not needed for execution (scala-swing, continuations, various source attachments) are added to sdt.core
* features need an extra step, because in 2.11 we need to ship two extra bundles (xml and parser combinators). This is done through the new -Pset-features profile in build-all.sh

As a bonus, all Scala bundles have correct source attachments now, so plugin
development should be much easier.

Fixed #1001889.
Reviewer comments:

- added Scala compiler sources
- added xml and combinator versions only in the 2.11 profile
- removed useless dependency on HasLogger
- removed exported dependencies from sdt.core project files
- removed superfluous version numbers in dependencies
- fixed runtime library for build-tools to always be 2.10
Merge pull request #565 from dragos/improvement/scala-osgi

Switch to vanilla Scala OSGi bundles