The first one is a stupid mistake due to the fact I was only testing with one
video at a time, so I didn't notice that the first item of the list was getting
deleted if the entry wasn't found.
The second one: I didn't like the `setInterval`, because I couldn't stop it, but
I didn't think of another solution first. Now the function calls itself with a
`setTimeout`, only when it knows the video hasn't ended yet — no infinite calls
anymore. And each time we get a new video, we `runResume()`, whith the
ResumeManager class handling the preferences.
This code can clearly be improved, but bug's fixed.
