Add remember me checkbox on login

**NOTE**: This depends on https://github.com/tidepool-org/platform-client/pull/16

Saves your session in the browser's local storage, that way when you hit refresh you are logged back in.

Logging out will destroy the session.

If saved token has become invalid, you are automatically redirected to login screen.

![screen shot 2014-05-05 at 7 32 11 pm](https://cloud.githubusercontent.com/assets/1306536/2880788/3a1e7c8c-d47b-11e3-94d7-a92b44a96985.png)