Mobile design cleanup

- consolidated login/registration to use the same css file and also a parent container class because they share the same styles
- fixed registration page & manage currencies page to be usable (still not great but better than before)

New:
![image](https://cloud.githubusercontent.com/assets/51415/4762224/41838cdc-5aff-11e4-8749-d77c84a4f3b9.png)
Old:
![image](https://cloud.githubusercontent.com/assets/51415/4762226/4d9a7c60-5aff-11e4-90f0-0523b9263613.png)

-----
Old:
![image](https://cloud.githubusercontent.com/assets/51415/4762246/8b107112-5aff-11e4-88ae-5649e9686266.png)

New:
![image](https://cloud.githubusercontent.com/assets/51415/4762255/ab22e304-5aff-11e4-9250-e21d135fbb7d.png)

That's on purpose Jared. That's because the bottom visual padding on desktop is too much, and if I do the same on mobile it doesn't support double lines for "Supported currencies for stellar.org:".