Add keyboard shortcuts for track editing

[lehnerpat]

When editing a track, I usually pan the map with the mouse, but want to use the keyboard to control the video player (play/pause, skip forward/back). Adding a new timing point also requires a mouse click.

When panning the map with the mouse, the map gets the input focus, so keyboard events don't go to the player. When clicking the player for input, the map loses focus. When clicking the "Add" button, neither the map nor the player have focus.

Let's add some keyboard shortcuts for the editing workflow, and add an input listener that grabs them even when manipulating the map with the mouse -- if possible?
Possible add a toggle button to enter/exit this "capture input" mode.