Easy way to replay given measures

[PolyMeilex]

We need to have a way to replay given measure, without messing with manual rewind. So either add a way to rewind by measure, or introduce some sort of auto looping of given measures.

[PolyMeilex]

Recently I introduced list of measures in MidiFile::measures field, so it should be relatively easy to implement now.

We can easily get the current measure by binary searching the list.

Perhaps we could also render the measures in the progress bar somehow, not sure how that would look like yet.