Add announcements -> dates association dependency
Add announcements -> dates association dependency

We should be destroying the dates when the announcements are destroyed.

robinwhittleton/whitehall,YOTOV-LIMITED/whitehall,alphagov/whitehall,alphagov/whitehall,askl56/whitehall,YOTOV-LIMITED/whitehall,robinwhittleton/whitehall,robinwhittleton/whitehall,alphagov/whitehall,ggoral/whitehall,ggoral/whitehall,askl56/whitehall,hotvulcan/whitehall,ggoral/whitehall,askl56/whitehall,robinwhittleton/whitehall,askl56/whitehall,YOTOV-LIMITED/whitehall,hotvulcan/whitehall,hotvulcan/whitehall,ggoral/whitehall,YOTOV-LIMITED/whitehall,alphagov/whitehall,hotvulcan/whitehall