Show member’s statement on card hover

**READY FOR REVIEW** Closes #2054 

With this change, when you hover over a .mini-user card on the homepage or a community page, you will see a truncated version of their statement. This only happens on devices without touch events.

**Testing note:** It would be awesome if someone had a touchscreen laptop to test this out. I’m not sure how it would behave on their right now

### Todo
- [x] Create or re-use a tooltip module
- [x] Fetch statement from new participants
- [x] Truncate statement to 140 characters
- [x] Append appropriate text whether participant is singular or plural
- [x] Fetch statement for givers and receivers
- [x] Styling changes to match Gittip
- [x] Create appropriate changes to schema
- [x] Cross browser/device testing
- [x] Disable tooltip when tapping on a mobile device
- [x] Test that “I am” or “We are” is properly appended for givers and receivers
- [x] Add tooltip to Community pages
- [x] Don’t show tooltip for anonymous cards
- [x] Debug hover event on hybrid touch devices
- [x] Move schema changes from `schema.sql` to `branch.sql`

![screen shot 2014-03-22 at 3 08 09 pm](https://f.cloud.github.com/assets/65468/2491640/7b8bf058-b1f5-11e3-896a-b1c75924cefa.png)