Calculate and show video frame number

[emilk]

What

Show frame number in selection panel when selecting a video.

We may want to make it more prominent though? 🤔

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[Wumpf]

We may want to make it more prominent though? 🤔

Yeah now that we're confident enough with this (I think we are!) this might be together with the expandy-area in "top-level" 🤔

[emilk]

I'll go with this: