[Added] lair mobs can now have variable weighting

[Added] unit tests to verify lair template's mobiles and boss mobiles
exist
[Added] unit tests to verify lair template's mobiles' weighting and boss
mobiles' counts are positive numbers
[Added] unit test to verify lair template's spawn limit is positive

Change-Id: I0ec7ab223361dae3fc5ba9c3434b20138fae48ba
Merge "[Added] lair mobs can now have variable weighting" into unstable