Overwrite player icon using config option

[mariuszste]

Since discord can accept any valid image URL as the icon for rich presence it would be nice to be able to overwrite that for any player. This is especially useful for new players that don't have an icon built in.

things to consider: how would this interact with #32
Discord actually has 2 slots for icons, so maybe we can put the player icon in the small circle one and the album over in the big one?

[FichteFoll]

Yes, it's a good idea to implement this together with #32.

[FichteFoll]

This is possible now via the client_id (de9d532) and icon (dbeed4f) configuration options. This does support HTTP URLs already, which I actually forgot to document, so I'm considering this to be done for the next release (whenever I get around to packaging that because I changed a few things that I'll need to test first and would also like to implement a few more things until then).

[mariuszste]

Awesome, thanks. Moving more things to the config is definitely welcome.