Admins create availabilities for their charity

https://trello.com/c/0qfz3zvZ/10-as-an-admin-i-can-create-availabilities-for-a-town-on-a-date

![image](https://cloud.githubusercontent.com/assets/8646429/5090022/179a56f4-6f0d-11e4-93ca-86144294908b.png)

Use the new Ruby 1.9 hash syntax.