added ABS as submodule

Removed included ABS sources and added as a submodule. 

This makes it easy to pull fixes directly from ABS, but also has some issues: 

 * cloning the project is now a bit harder: you have to remember to ```git submodule init``` and ```git submodule update``` to actually get all the code
 * the submodule is just a pointer to the remote commit, so if you update, you need to remember to push in order to update the pointer. This makes sure everyone is using the same ABS code.
 * we can't really push changes to ABS remotely (like `lint.xml`, etc.), only make local changes (or I just haven't figured out how to do it properly)

More info: http://git-scm.com/book/en/Git-Tools-Submodules

Not merging this for now, so people can comment/review.