Signup Page UI Redesign

[akhil-rana]

The new design matches consistently with the whole application.
Some changes are:

1. Improved email text field validation.
2. The "id" attribute was missing in the email "input" which caused in "can't read property of null". Now it's fixed.
3. Dropdown select option for user type has been added instead of previously used radio buttons.
4. Addition of bootstrap, fontawesome (for icons)

[birm]

I think this is fine for now since it sidesteps #254 entirely. @nanli-emory has the real review power here though