Change play/stop icons

[emiham]

This is probably the most minor issue ever, so feel free to close it right away, but I've noticed that for some users (n = 1) the play and stop icons are very confusing. It's easy to misunderstand as somehow controlling the music and not spawning a new player, especially if you didn't set up the system yourself (this all stems from me setting up Snapcast for my dad). Unfortunately I personally can't really think of a more appropriate icon, but I thought it's worth letting you know at least.