Improved death messages for PK battles

[gmriggs]

Improved death message system to include death messages from other perspectives: the attacker, the victim, and nearby players

• Added /sticky command - prevents players from leaving corpses and losing items on death
• Fixed /heal to use max vitals
• Added /deathxp command
• Added randomized death messages for monsters killing players, based on damage type
• Fixed a bug where spell projectiles weren't triggering the critical death messages
• Improved the generic creature -> player death pipeline
• Fixed a bug where monsters would continually attack players while still materializing at the lifestone