Make startup faster

[zdimension]

POI:

• import mainwindow.py = 2 seconds on my machine = way too slow
• mainwindow.init_main = ~15 seconds on my machine = damn
  • init_ui = 14 seconds
  • change_language = ~3 seconds

[zdimension]

With 19ad904 and bb5e652 we're now down from 17 seconds to 6 seconds

[zdimension]

from pyqode.core import api takes 12 seconds somehow