Fixed some issues regarding wxPython errors and ffmpeg-rendering

* setlocale has to be None on my system - not sure why? I'm using wxPython 2.9.5.0
* RefreshMenu is throwing errors every time it is called, because wxPython on mac does not set the title of the menu implicitly
* replaced time.clock() with timeit.default_timer() - clock() had some timing issues on mac
+ added focusCorrection for Fullscreen - but I still haven't managed to fetch the initial focus - you have to click once on the image, then the shortcuts you defined work in fullscreen
* changed ffmpeg parsing

I think GIFs should be parsed manually again, because ffmpeg does not detect their video-length correctly at all times