Better Boss Expansion

NPCs
- Added new boss fight: Elemental Guardian
  A three-phase boss that shifts between Earth, Frost and Flame
- Elite Revenant Guardian now drops its sword

World
- Added new Orbis fragment: Ancient Elemental Temple
  An instance with the dormant Elemental Guardian - wake it with
  Elemental Awakening Dust.

Items
- Added Fragment: Orbis - Ancient Elemental Temple
  (crafted at the Arcane Workbench from a green, a blue and a red crystal shard)
- Added Elemental Awakening Dust
  (crafted at the Arcane Workbench from emerald, ruby and sapphire)
- Added Elemental Rune Shard dropped by Elemental Guardian
- Added three runes, each crafted from one Elemental Rune Shard at a powered Goblin Lab:
  - Tornado Rune: summons a stationary tornado
  - Ice Breath Rune: breathes a stream of frost
  - Flame Shockwave Rune: releases a shockwave of flames