Fixes to all current issues: Ui_refactor0

[jonnyhyman]

This pull request makes changes mostly to editor.py, for issues #4 #5 #6 #7

• Undo / redo buffer return to Qt Control
• Tabbing and de-tabbing shortcuts and logic (no selection tabbing yet though)
• Window width can be much smaller now
• Scroll issue Scroll stops working occasionally #5 was caused by the undo/redo algorithm (deprecated in this release)