Mouse events (context menu + hover)

[Nikolay]

1. "CONTEXT MENU" (right-click) event.
It shall fire AFTER selection has already changed (unlinke today's "right mouse up" event),
i.e. when the context menu is about to be shown.

2. "MOUSE HOVER" events.
They shall fire when user hovers over a shape, when cursor leaves the shape, something like that. The shape over which the cursor is hovering shall be passed as event parameters. Today's "mouse move" event is no good because it needs kinda "weird" arithmetics to figure out the shape cursor hovers over.