New proposal
- Horizontal header
- click: switch time + select frame of the current layer
- rclick: menu (insert/remove columns)
- click+drag: switch time + select frame of the current layer (scribble)
- shift+click: select column
- shift+click+drag: selection multiple columns
- Vertical header
- click: select layer
- rclick: menu (add/remove layer, show/hide layer)
- Frames Table: empty area.
- click: select single frame + switch time + *don't* switch layer
- rclick: menu (insert/copy frame)
- click+drag: scrubbing + switch time + *don't* switch layer
- shift + click + drag: select multiple frames + switch time to the latest + *don't* switch layer
- Frames Table: area on existent frame.
- click: select single frame + switch time + *don't* switch layer
- rclick: menu (remove frame)
- click+drag: *move* a frame or multiple frames
- ctrl + click + drag: *copy* a frame or multiple frames
- shift + click + drag: select multiple frames + switch time to the latest + *don't* switch layer
- alt + click+drag: shift the frame and all its right-hand-side frames to the right or to the left until the previous keyframe (stretch the previous frame)
- Frames Table: all
- space+click: pan
- space+rclick: zoom