Split up the single Eclipse feature into a 'runtime feature' and a 'meta tooling feature'

This is some initial work on http://yellowgrass.org/issue/Spoofax/845

I added a feature `org.strategoxt.imp.meta` and moved as many of the meta languages from `org.strategoxt.imp` to `org.strategoxt.imp.meta`. Features that are part of `org.strategoxt.imp.meta` will be installed when you install Spoofax, but they won't be installed when you install a deployed Spoofax language.

- We can slowly move more plugins over, such as the generator. 
- It's tested and backwards compatible, but let me know if it still breaks something.
- These are the languages that are still part of `org.strategoxt.imp`: DynamicRoot, Stratego-Sugar, prefspecs, DynamicRootInitializer, LPG, psp
  - I still have to figure out which of the plug-in pulls in Stratego-Sugar.
  - DynamicRoot, prefspecs and DynamicRootInitializer may be IMP things. We can ignore those for now.
  - Still have to figure out what the LPG and psp languages are.