CanvasMainWindow: Fix initialization of QAction
CanvasMainWindow: Fix initialization of QAction

Setting both the `checkable` and `checked` properties by constructor
keyword arguments (a PyQt feature) does not work reliably (depends on
the dictionary traversal order - i.e. the checked property is
unsuccessfully set before the action is made checkable).

qPCR4vir/orange3,cheral/orange3,kwikadi/orange3,marinkaz/orange3,kwikadi/orange3,marinkaz/orange3,kwikadi/orange3,cheral/orange3,kwikadi/orange3,kwikadi/orange3,qPCR4vir/orange3,cheral/orange3,cheral/orange3,qPCR4vir/orange3,cheral/orange3,kwikadi/orange3,qPCR4vir/orange3,marinkaz/orange3,cheral/orange3,qPCR4vir/orange3,qPCR4vir/orange3,marinkaz/orange3,marinkaz/orange3,marinkaz/orange3