Console|libcommon: Updated 'server-game-episode', 'server-game-map' wrt custom episodes

server-game-episode is now a string. server-game-map is now a URI.
Any server configurations will need to be updated accordingly.

Both variables are only registered when running in dedicated server
mode. Note that the client will warn about these now unknown cvars
when updating due to their presence in old cfg files. Such warnings
can be safely ignored.