show playback position on thumbnail (progress) + history page

[tzarebczan]

Also on history page:

• clear items (all vs single)
• add setting to disable history

Something to consider:

• saving position in really short files
• if you're 90%+ into a file, may not want to start where you left off (also based on length - shorter should have their own limit)

[ktprograms]

Maybe something like 6 (or maybe 10, will have to see how long videos have non-"content" for) seconds or 90%, whichever is longer. (So short videos will still have a sensible minimum)

Should probably also have an upper bound so a 1h+ video will still limit to maybe last 30s.