Reorg

Some reoganization for the mavlink repo that mostly affects pymavlink (see https://groups.google.com/forum/?fromgroups=#!topic/mavlink/Qtylf_u3XPU).

* Created a tools/ folder for pymavlink/generator, generator_gui, and pymavlink/mavplayback
* Moved pymavlink/examples to examples/python and moved the rotmat.py library into pymavlink/
* Fixed python import paths for everything in tools/ and examples/python/
* Cleaned up and consolidated .gitignore files