Resize window

[hannesdelbeke]

• window now correctly remembers size, position, fullscreen, maximised state from previous session.
  this was currently prevented by the crash on exit. Not freed memory blocks on blender close #47
  • removed atexit module and on_exit method. since we could simplify the code
  • did not solve the crash on exit, for further debate on this see above linked issue
• window now maintains the dimensions of the unwrapped blender window, if it was never wrapped before
  solving first time qt window size is too small #72
• refactored some docstrings and constants

note

• full screen or maximised state are not yet passed on first time wrap.
  seems overkill but we could always add it.