First version of maze.
Known bugs:
-Rotation from NORTH to EAST or EAST to NORTH
-No green and red color on cells where tux is gone through
-Sounds not tested
-Transition in fast track mode
Merge branch 'master' of git@git-next.kde.org:kde/gcompris.git into maze

Conflicts:
	GCompris.pro
Better rotation
Correction for better animation in fast mode
maze, better maze sizing for vertical screens
Button for invisible maze
Merge branch 'maze' of git@git-next.kde.org:kde/gcompris.git into maze
Compatibility with tablet
maze, minor, wrap the message in invisible mode
With button for tablet
Merge branch 'maze' of git@git-next.kde.org:kde/gcompris.git into maze
maze, centered vertically the maze
maze, larger on screen arrows to acomodate mobile
New icons for relative mode.
Move icons are now visible only on tablets.
Merge branch 'maze' of git@git-next.kde.org:kde/gcompris.git into maze

Conflicts:
	src/activities/maze/Maze.qml
maze, better position for the switch mode message
core, minor, smaller min window width to ease testing

Makes it easier to test vertical screen.
gletters, minor changes

- added a global uri
- Set the background image in Image.PreserveAspectCrop
mosaic, created a specific vertical layout
First version of color_mix et color_mix_light