[c12670] Add missing spell id 21883
Credit to xfurry
[c12671] Implement ACTION_T_CHANGE_MOVEMENT for EventAI
This will allow changing the creature movement based on eventAI events.
Note: action is #48 in cmangos but #49 in mangos two

Credits to xfurry
[c12672] Implement SCRIPT_COMMAND_SEND_AI_EVENT_AROUND for dbscripts
engine
This allows more flexibility in the interactions between eventAI and
dbscripts
Credit to xfurry