Added undo/redo framework base
Added create command implementation
Added primary create/remove command implementation
Added undo stack respectivity to digram
Added links processing when creating and removing
Added can undo/redo actions state and modifications state processing;
Added primary resize, move and change parent undo/redo
Added durable to parent state modifying child state modifying
Merge branch 'master' of https://github.com/qreal/qreal into undoredo
Fixed segfault in some resize cases;
Added fold command
Added base links reshaping undo/redo
Added some missed commands
Fixed wrong graph transformations includes
Fixed links incorrect behaviour
Fixed edge gesture creation undo/redo
Visibility conditions added. It is possible to specify one enum property to be a visibility condition to an item of a shape
Merge branch 'master' of https://github.com/qreal/qreal
visibility conditions load fix
Added linker actions undo/redo
Fixed some gestures segfaults