Libelemate, google test, upgrade to glow 0.3.0+

- This integrates the google test framework, ref #114. All the important elemate code is now part of the "libelemate", allowing us to link our code against the test executable.
- The game executable/target project is "elemate", just as before. (For VS: set the working dir to ../..)
- you can run the test via the elemate_tests target

This upgrades elemate to glow 0.3.0, older versions will not with this pullrequest. I would suggest that we use a newer version than 0.3.0, at least https://github.com/hpicgs/glow/commit/89e03d624c789db4403aab6f88c2649267d6ee6d, as it support glBufferStorage (used by our terrain) and fixes some warnings in the glow::Buffer.