KonsolScript and Game Engine Code

* implemented Export PNG with non-transparent background
* minor fix on ffmpeg not being called on Windows even if on PATH environment_variable; requires ffmpeg located along with Kage Studio
* fixed error on exporting video with lower frame count than FPS settings
* fixed errors in saving Kage Studio File
* fixed error on calling non-existing external command on GNU/Linux
* renamed Makefile to Makefile.win
* some code-cleanup