458 contextual menus for keyframe widget indicators - progress

contextual menu is displayed with usual kf actions (add/remove/duplicate/properties)

tofix : current time is used in place of time line mouse position
458 contextual menus for keyframe widget indicators - progress 2

- remove parent "keyframe" menu to only display keyframe actions
458 contextual menus for keyframe widget indicators - progress 3

- comment unnecessary code.
458 contextual menus for keyframe widget indicators - progress 4

- add keyframe toggle to context menu
458 contextual menus for keyframe widget indicators - progress 5

- undo de21869cbab619
458 contextual menus for keyframe widget indicators - progress 6

- prepare keyframe set description
- micro optimize and rationalize activation (set_sensitive) of actions by using variables
458 contextual menus for keyframe widget indicators - progress 7

- improve keyframe actions activation
Fix 458 contextual menus for keyframe widget indicators (progress 8)

- keyframe set description