Ripple insert or delete time.

Inserting time would move all timed things in the scene (keyframes, sequencer strips, mask animations, markers and frame ranges in modfiers and drivers) after the current frame by a number of frames input by user. If the input is negative, all frames in the range after the current frame should be deleted and the remaining, pulled back. Option to input frame ranges would also be nice (insert/delete from frame-x to frame-y). Sequencer strips should be split where needed.

This would be a time-saver for those who have to move around frames in more than one timeline window (say Grease-Pencil dopesheet, regular dopesheet and the VSE) to edit the timing of the scene.