EMI: Save and restore chore instance IDs.

Previously chore instance IDs stored as Lua userdata became invalid after
loading a save, because the chores were recreated with different IDs. This
caused certain opcodes like StopChore to fail.
EMI: Fix compatibility with older savegames.
Merge pull request #911 from Akz-/emi-save-animation

EMI: Save/restore fixes