Merge branch 'develop'
Add missing license headers
Update README.rst
Cleanup screenshots
Update README.rst

Update screenshot branch path
Cleanup screenshots
Update README.rst
Update README.rst
Fix performance issue with visible blocks (all blocks were considered as visible)
Fix issue with slow document words comletion #57
Fix loading issues #57
Fix saving issues: optimize cleanupText and rename it into cleanupDocument #57
Rm dbg msg
Adapt delay
Fix issues with dirty changed introduced by the last changes to cleanupDocument
Optimize __fold
Fix performance issue with checker: cloning the document takes a lot of time
Rm dbg msg
Fix index out of range when selection inverts -> nothing is selectable
#62 fix panels offsets on all major linux desktop envirronement:
  - tested on unity, gnome, kde and cinnamon
  - need to test on Windows 7 and Windows Xp