Merge pull request #100 from Waldteufel/osx

Use OpenGL 3 and adapt for OS X usage
UTIL: Remove Semaphore and ReadWriteLock classes

Both are currently unused and could be reimplemented in a platform independent
way using the C++11 thread support library.
UTIL: add get_settings_path
UMVE: Implement OS dependent search paths

- Added new namespace umve
- Implemented umve::get_search_paths() which pushes OS dependent search paths into a given vector
- Use umve::get_search_paths() for plugins and shaders