- class CGuiHandler is now called GameEngine to better describe its
functionality
- renamed global GH to more clear ENGINE
- GH/ENGINE is now unique_ptr to make construction / deconstruction
order more clear and to allow interface / implementation split
- CGuiHandler.cpp/h is now called GameEngine.cpp/h and located in root
directory of client dir
Fixes two bugs, one was definitely happening, and 2nd one that is causing
undefined behavior and may work only in some std implementations
- VideoPlayer would attempt to access subtitles widget after VideoPlayer
itself was destroyed in onPlaybackFinished call
- std::function was destroyed from a function that is being called by
it. Replaced with 1-method interface to avoid usage of std::function in
this scenario
