Mobile viewing optimizations

This includes a change to access the page from a mobile device as well as some new CSS rules to make the card reviewing page look good on a portrait-mode phone. I hid the actual queue of completed cards since I thought that information was not critical.

It looks like this.

![screen shot 2014-07-18 at 10 04 51 pm](https://cloud.githubusercontent.com/assets/2415796/3633885/41d84504-0f02-11e4-84ed-ae64f670a2ac.png)

Next up:
- Debug style on an actual device, this is just the emulator and on my actual device it was a little difficult to click the "easy" and "hard" buttons, so I think I need to make them larger.
- Re-styling the nav bar
- Figuring out why the "make more" and "continue practicing" links do nothing