Twitch Spawn

Added
- New "Mobs" screen: lists every mob in the game (modded ones included) with separate ON/OFF switches for the Mystery list (eggs and Mystery Spawn) and the Passive list (Animal Surprise). Filter by type (hostile / passive / other) and by mod, or search by name. Bulk "all ON / all OFF" buttons apply to the current filter.
- New "Mystery Spawn" rule: a reward that spawns a random mob from the Mystery list around the player.
- Missing default rules (Mystery Egg, Mystery Spawn, Animal Surprise) are added once to older config files.
- Likely bosses are unticked by default in the Mobs screen (Forge "bosses" tag or boss/dragon/wither/warden/giant/leviathan in the id). Best effort, please review.
- A "Twitch Spawn" button in the Options screen (only while in a world). The K key still works.

Changed
- Spawned mobs are now named after the viewer only (e.g. "Pseudo" instead of "Zombie de Pseudo"). The viewerNameFormat setting is no longer used.
- The Mystery list is now the only reference once the Mobs screen has been opened (an empty list means no mob, instead of "all vanilla mobs").

Removed
- The "Twitch" button in the pause menu.