Add a new button to the controls that defines whether the media repeats
at the end of the stream. The states are:
- Disabled: Media does not repeat. This is existing behavior and the
default state.
- Always: Media always repeats.
- Once: Media repeats once. Flag is reset when loading new media.
Tested all three states with both audio and video.
Added a `rustfmt.toml` to avoid reordering imports. They keep moving
around in previous pull requests, best to just define what we want in
the repository.
Fixes: #39
