-f for `/play` to add to the start of the queue instead of the end

[macdja38]

Adding the flag of -f should insert a song at the beginning of the queue instead of the end.

This is a decent first issue, though knowledge of the rethinkdb api would be a useful pre requisite though the api is decently straight forward if you're at all familiar with .forEach / map style functional constructs and fluent apis.