Add new column `search_radius` to `creature_linking_template`.
If this column is used (value > 0), master and slave are linked together if and only if they have their respawn coordinates within this range (point-to-point distance calculation)
Note that linked spawning is slower this way and should only be used if required
Signed-off-by: Schmoozerd <schmoozerd@scriptdev2.com>
