Добавлено выделение редактируемого лэйбла по f2

По нажатию F2 при выделенном блоке должно включаться редактирование
первого редактируемого лейбла на сцене для этого блока
Edited selection of the label by pressing F2
Merge branch 'master' of https://github.com/artbez/qreal
Some inconsistent code migration
Merge branch 'master' of github.com:qreal/qreal into 2d-model-code-improvement
changed code in conformity with stylegide
fixed a bug
Supported attribute "override" for ports.
Small remarks in supported "override"
Supported attribute "override" for ports.
merge branches and removal conflicts
merge branches [2]
supported generalizations for "pictures" and "labels"
Merge branch 'master' into override
Some bugfixes:
- swaped real and unreal update intervals;
- wheels in TRIK robot picture moved to back;
- 2D model is now again automaticly shown on interpretation start
- Repaired draw line and circle blocks
- Fixed linker`s floating segfault
Merge branch 'master' of github.com:qreal/qreal into robots
Removed color enumerations, used QColor(QString) instead
Accomplished moving large pieces of code from D2ModelWidget to D2ModelScene
Fixed world loading issues.
Fixed incorrect robot`s position resetting when clearing.
Merge branch 'master' of github.com:qreal/qreal into 2d-model-code-improvement