Brush resizing is now interactive

Now, brush and eraser sizes can be changed by pressing SHIFT while
dragging the mouse (like in Krita)
shortcuts fix/patch to make them work on windows
Merge pull request #59 from eVoLuTiVeMEDIA/shortcuts-fixes-for-windows-

1. Brush resizing is now interactive  2. Shortcuts fixes
Merge branch 'master' of https://github.com/pencil2d/pencil

Conflicts:
	src/interface/toolset.cpp