new version (0.14): Introducing 2x2 mode and colour protect filters

This version introduces 2 tools that been in my sights for a long time. 
-2x2 edit mode. This new CHR editor mode works in a for the NES oftentimes "natural" chunk of 2x2 tiles at a time. This covers the convenience gap between the normal 1x1 mode and the free draw mode (drawing on the canvas, which isn't this tools main focus). 
-Colour protect modes: Each color index can be write protected. In practice, this means you can now draw without messing up colours you don't want edited. It also happens to work rather smoothly as a tool for drawing or pasting "behind" already existing patterns - a bit like layers, but without having to manage layers. (It's not really like layers, since you can't store pixels behind other pixels in NES native work formats, but this comes pretty close). 

There's also some general GUI and CPU improvements. The canvas menu is easier to browse. The CHR editor has been fitted with more status readouts. There's a few new actions, bugfixes etc too. Please view the changelog for more information. 

I'll update the Keyboard cheat sheets inbetween this update and the next.