Finally fixed - Tablet with pen in relative mode is now drawing correctly.

Now, pencil seems to be the unique open source drawing software
accepting tablet relative/mouse mode with pressure.
keypress improvements + code simplification + refactor
Merge pull request #180 from eVoLuTiVeMEDIA/master

some changes
Tooltip updates
Remove last unused comments
Mobile color palette improvements

1. As color palette is not really a temporary tool (given that
visibility is switched)
shortcut key was changed to [C] ; It seems even easier, more intuitive,
and safer.
2. Mobile color palette is now a window.
3. Main keyPressEvent() changed to keyPressed(), for a more flexible
access from other window's keyPressEvents.
popup color palette window flags & code refactor

Note: Color changes when you close window by pressing [x] button
or press c key
Merge pull request #181 from eVoLuTiVeMEDIA/master

Some usability improvements and code cleaning
Merge branch 'master' of https://github.com/pencil2d/pencil