Repository layout restructuring

The branche introduces a new layout of the openms repository that should enable us to further decouple the individual parts of OpenMS. The basic discussion was already performed on the mailing list

Some notes:

 * everything compiles, tests pass (except AccurateMassSearch) docu works, checker works
 * ~~pyOpenMS was not tested (yet) but should work (test build is currently running, I add a comment as soon as the build is through)~~ works see f070cdcc40ecdfea7b7cf41932978dab1828e9a7
 * the gui tools are still part of openms_gui since they cannot be that easily decoupled, the rest is separated as planned
 * their is an unrelated commit in the pull request that adds proper forward declarations to DataValue (5f05f71a5be0b403607c8316db4702e2109bd623). It landed accidentally in the branch. I can also move it out and put in on develop as soon as the pull request is through but it is not that intrusive as it was (due to the removal of the list classes) so I left it in