Move more to Lua side

Updated to remove the logic from C code and make Discord's RPC fields directly settable from Lua.
This is much more flexible and powerful and is how it should have been done before.

Note: Discord RPC seems to down for Windows right now so I've been unable to test that. Other apps are failing to connect too even after restarts and reinstalling so I'm pretty sure it's not me!

Edit: Windows problem is gone and all works good!