special case for upgrading herald with weapon master into lord of change with weapon master (melee)

Greater demon immortality enable.

Added functionality to make greater demons immortal, but the api doesn't work, or at least I can't figure it out.
Added a limiter of 10 attempts to the problematic Lords (dedicating Sorcerer Lords to Nurgle or Tzeentch), as these have trouble with their background skills.
Increased the general limiter to 100 attempts.

AI factions will not attempt to get the same background skill.
The script will only attempt to get the desired background skill 30 times before giving up.