Fixes to several bugs

- Some small fixes to white deer
- Fixed pz bug at {x = 33007, y = 31231, z = 6}, fixes #633
- Added fury gates AIDs, fixes #632
- Unlocked door at {x = 32999, y = 32096, z = 6}, fixes #621
- Added GH Low Waters Observatory and fixeds it stair, ref #323
- Added 2 giant spiders to the cave at {x = 32878, y = 32661, z = 10} #602
- Changed medusa into serpent spanw at {x = 32873, y = 32623, z = 11} #602
- Added solo demon at {x = 33068, y = 31720, z = 14} and {x = 33068, y = 31720, z = 13} #536
- Added two demons at {x = 33068, y = 31720, z = 12} and removed fire elementals #536
- Added demon instead of fire elemental at {x = 33120, y = 31724, z = 14} #536
- Changed Yalahari monster file since someones RME keep changing creature into NPC, same with Armenius
- Small tweaks to spawn.xml
- Updated dreadbeast and hellgorak, so you can close #560 and #561 since this guy got inactive
- Added AID 50027 to the lever that create a bridge to exit hellgate #489