Better error pages in the login flow

Assign: @natebrennand 

The "log out" button will disconnect their account, so that they will have to re-auth.

If we didn't whitelist their email:
![screen shot 2014-09-28 at 1 43 13 am](https://cloud.githubusercontent.com/assets/2433509/4433388/ae2363ae-46d6-11e4-8f8c-801198f82f58.png)

Any other errors:
![screen shot 2014-09-28 at 1 42 59 am](https://cloud.githubusercontent.com/assets/2433509/4433389/ae23b6e2-46d6-11e4-965c-76e19e7238d3.png)

Successful login:
![screen shot 2014-09-28 at 1 51 23 am](https://cloud.githubusercontent.com/assets/2433509/4433390/ae2ace14-46d6-11e4-803a-7cf6ba3f390c.png)

to elaborate, it's generally a bad idea to use an arbitrary number as a constant.
it's complicated a bit since it needs to be coordinated between the frontend and backend code but I still think it'd be better to have a constants defined in groups on both. As long as this is the only number, the constants could just be at the top of both relevant files. If there are more later on, a full file to hold all of them might be more manageable so that there is not reuse in the numbers.