This commit is a minor refactor of how arenas are resolved by name,
similar to the previous arena class resolution refactoring.
The difference this time around is that there is an ArenaMaster method
that does most of the work for a lot of different areas of the plugin,
`getArenaWithName(String)`. This method is called from well over 30
different places in the code base, making it a cornerstone of all arena
resolution. Luckily, it is called primarily from places that shouldn't
care _how_ an arena is resolved.
Affected by this commit are all commands that resolve arenas by name,
including all those not listed in the diff, because of the change to
`getArenaWithName(String)` on ArenaMaster.
Commands that can tab complete arena name arguments now complete slugs
instead of config names.
Andreas Troelsen
0f93d8ac05