Add organizations to the volunteer db

**DO NOT MERGE**  This needs styling and some minor tweaks to when certain links are shown to organization admins.

### What is the problem / feature ?

There were no organizations!

### How did it get fixed / implemented ?

Added a bunch of stuff for the following functionality.

- Creation of closed and open organization.
- Administration of organization members.
- Request system for joining organizations
- Leaderboard based on organization member volunteer hours.

### How can someone test / see it ?

- See the new organizations top-nav menu item.
- Create an organization.
- Claim some shifts
- See the leaderboard

*Here is a cute baby animal picture for your troubles...*

![tumblr_m2hzvach0i1qi0jmeo1_1280](https://cloud.githubusercontent.com/assets/824194/2686383/c551f694-c1fc-11e3-841f-17b6ad7dc9a1.jpg)