[Feature] Change Login Splash Screen and Artist Credit within Admin UI

[takemurahusky]

Pretty much what the title is saying.
That way we don't have to create a new release every time the splash needs to be changed.

[Thiritin]

Likely a good idea to do as part of the new conventions feature.

[Thiritin]

Added to the conventions feature but will add once we got the data in on live for a few months so we implement it on next EF for realsies.