Allow de-selecting thumbs up and down

Currently once a message has been given a thumbs up or down, it's impossible to then deselect the vote - all you can do is change it to the other one.

For example let's say you give a message a thumbs down but then decide to reroll it instead. The thumbs down stays selected on the new message and you're forced to either leave it or change it to a thumbs up.

Clicking on an existing vote should deselect it and rerolls should clear the vote state. It makes sense for the vote to remain selected after editing though.