Added marker blocks to robots metamodel
Added marker device and marker blocks;
All base blocks for trivial work with pre-configured devices are now generalized to 1 template block.
Added drawing robot`s trace on 2D model scene
Added clear robot trace button
Added customizing robot marker width in pen panel
Corrected PrepareMarker block labels coordinates
Fixed crash when attempting to generate code for second thread with if block
Added new button tool tip translation to 2D model
Merge branch 'master' of github.com:qreal/qreal into markers

Conflicts:
	plugins/robots/interpreters/trikKitInterpreter/src/blocks/details/ledBlock.cpp
PrepareMarker and RemoveMarker renamed to MarkerDown and MarkerUp
Merge branch 'master' of github.com:qreal/qreal into markers
Default robot trace width made 6 px.
Removed extra character
Merge branch 'markers' of git://github.com/dvvrd/qreal
Small styleguide fixes