Improve Administrator Panel

Significant functional and display improvements to charity administrator panel

![adminpanel](https://cloud.githubusercontent.com/assets/8646429/5247704/cd13751c-7942-11e4-8900-5966f2a06cb4.gif)

36000? => 10 hours. Is that your intended code? Either way, please extract to a named constant to clarify.

Also, this should be defined as a class method on Availability, and then can still be accessed as `charity.availabilities.recent`, but also used anywhere else