[z1964] Add support for range dependend slave/master

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>
Signed-off-by: Nighoo <nighoo@gmail.com>

(based on commit 839d83c)
(based on commit 6904541)

(cleaned version of e672205)

(based on commit [s1552] - a0855a5)