Replace Radioplayer button with an in-page player

[ashhhleyyy]

The URY Player(tm)

[ashhhleyyy]

Things still to do:

• [ ] Show current time from playback (including the 15s online delay)
• [ ] Scrubbing support through the local buffer
• [ ] Close button
• [x] Make send message form not refresh the page

Update: removed scrubbing support from this initial version

[ashhhleyyy]

Just needs some fixup on the mobile CSS (or alternatively, just use radioplayer on mobile)

[ashhhleyyy]

Here's what the final thing looks like:

And on mobile:

[alyxbb]

is the send message updates a duplicate of #292?