[12670] Add missing spell id 21883

Close scriptdev2/scriptdev2#106
[12671] Implement ACTION_T_CHANGE_MOVEMENT for EventAI

This will allow changing the creature movement based on eventAI events.

Requested in scriptdev2/scriptdev2-cata#4
[12672] Implement SCRIPT_COMMAND_SEND_AI_EVENT_AROUND for dbscripts engine

This allows more flexibility in interaction between eventAI and dbscripts
[12673] Implement spell effect 42281
[12674] Implement script library hook for NpcSpellClick

Close cmangos/issues#428