Implement authorization

Addresses issue #6 
Implements authorization so that people without valid uni's can't access the data.
Note: You need to put client_secrets.json inside the density folder.
You either need to check the length or (preferably) a regex that guarantees length.
Also, we must check if they are a barnard address as well.

something like:
```
"^[\w_\d]+@(columbia|barnard)\.edu$
```