Always show label tooltips

[mzur]

Implement the "hover", "always" and "off" state for the label tooltip in the image and video annotation tools (described here). The positioning of the tooltips (especially for moving video annotations) may be non-trivial.

[dlangenk]

For video: We could turn off the tooltips while the video is playing. Of course it would be nice to have moving boxes + tooltips, but I guess in most cases, it would should be sufficient to show them only on pause.

[mzur]

Good point 👍