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.
I did not fully think this though when I suggested it to you, uni can only consist of `[a-z\d]`. I think we should also allow for columbia addresses like ...@cs.columbia.edu

```python
regex = re.match("^(?P<uni>[a-z\d]+)@.*(columbia|barnard)\.edu$", email)
```

thoughts?