Fixed segfault on division by zero in expression parser
Added element deletion from scene by strike-out gesture
Implemented cutting on diagrams
Added port hints into 2D model sensors to distinguish them
2D model port hints made visible only by hover
Added touch-optimized mode settings
Added on-screen keyboard showing when focusing some editor in touch mode
Merge pull request #1234 from dvvrd/robots

Some usability features for RoboFest
Merge branch 'master' of https://github.com/qreal/qreal into trikDemos
renamed ports A, B and C to 1, 3 and 4 respectively, so that 2d model matches real TRIK robot. "Power motor" property is now true by default (as current dem model uses power motors) and default ports are changed to 3 and 4.