Eileen/csv

refs #136 
- can select purchases and download as csv
- partners with new purchases showing badges + top of list
- new `is_approved` column for purchases
- update `is_approved` for all new purchases downloaded
I think this is going to lead to a bug. When a `Purchase` is created the `is_approved` field is set to `nil` not `false`, so you're going to have to set up an initialization function so that it has the behavior you want.

```
def Purchase < ActiveRecord::Base
after_initialize :init

def init
  is_approved ||= true
end
```