Request: Show frame count / duration of selected range

[gkertai]

When I mark an in/out range, it would be nice to see how many frames/seconds I have selected. Possibly inside the timecode pop-up.

[gregcotten]

I like this idea

[gkertai]

This could also make marker durations more useful (see #54) if there was a way to add a marker to the selected range.

E.g. I would hit I to mark in, play back a few frames, hit O to mark out, then hit ⇧M to create a marker for the selected range. The I/O range could clear automatically (as per preference), or I might hit ⌥X to clear it manually.