Fix setup issue and remove region expansion

This commit consists of two components:
- Restarts are no longer required after setting up the first arena
- Regions no longer auto-expand

The restart requirement is fixed by preventing the ArenaMaster from
actually creating an Arena object and assigning it to the selected
arena upon generating the default arena node in the config-file. The
problem was that the selected arena was set to this initial Arena
object, but another Arena object was created afterwards, which due
to the equals() method of ArenaImpl overwrote the previously created
Arena object in the arenas-list, but didn't change the reference in
the selected arena. In other words; two identical Arena objects were
created, but used in different places (arena list vs. selected arena).

The auto-expansion is removed by simply never auto-expanding regions
upon setting the arena warp or spawnpoints. Instead, setting these
warps throws an error, if p1 and p2 have not yet been set, or if the
location is outside the region.