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)

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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)

If we're using combined styles for just the front form pages (don't know what's a good semantic name), they should have their own .scss file, hence for all the reasons I've chosen to use registration.scss to be that way for now, unless you have a better name to call them? The two pages are essential twins.