Initial commit of new gui framework for touchscreens
Merge branch 'develop' into feature/gui
implement getStringWidth() for xpcc::GraphicDisplay
center button text
Gui:
  * added Logger on USART2 (A2/A3)
  * use hardcoded calibration points
Gui: image displaying example
Merge branch 'develop' of https://github.com/roboterclubaachen/xpcc into feature/gui
gui: fix inlcusion error
gui: add linux hosted example using SDL
Merge branch 'develop' into feature/gui
Merge branch 'develop' into feature/gui
gui: implement IntegerRocker widget. various changes in whole gui
Merge branch 'develop' into feature/gui
gui: fix warning
WIP: implement AsyncEvent
doubly linked list: fix bug in erase() and add description
Merge branch 'develop' into feature/gui

Conflicts:
	src/xpcc/container/doubly_linked_list.hpp
	src/xpcc/container/doubly_linked_list_impl.hpp
Merge branch 'feature/gui' of https://github.com/roboterclubaachen/xpcc into feature/gui
gui: suppress compiler warnings
doubly linked list: add warning to erase()