Mobile browser enhancements

Make the bar at the bottom appear at the bottom of the page if there is room, like a full-page responsive site

![screen shot 2014-04-26 at 3 41 33 pm](https://cloud.githubusercontent.com/assets/192620/2809652/e8e225a0-cd7a-11e3-86a6-7da61f6afccf.png)
![screen shot 2014-04-26 at 3 41 39 pm](https://cloud.githubusercontent.com/assets/192620/2809653/e8e3cbb2-cd7a-11e3-8d27-2ee79469f201.png)

When there isn't room, have it default to it's previous behavior of appearing in place

![screen shot 2014-04-26 at 3 41 50 pm](https://cloud.githubusercontent.com/assets/192620/2809655/e8e494ac-cd7a-11e3-894c-e00cf7691531.png)

Fix the second video that, in mobile browsers where the width < 400px, was causing a scrollbar.

![screen shot 2014-04-26 at 3 42 01 pm](https://cloud.githubusercontent.com/assets/192620/2809654/e8e408c0-cd7a-11e3-9a70-eefe152d9948.png)

Make the bottom buttons smaller and in a 2x2 grid layout when there is room.

![screen shot 2014-04-26 at 3 42 10 pm](https://cloud.githubusercontent.com/assets/192620/2809656/e8e549b0-cd7a-11e3-83e0-1fb27afb15d1.png)

Add a padding at the bottom of the page so the footer is always visible over the share icons.

![screen shot 2014-04-26 at 3 42 17 pm](https://cloud.githubusercontent.com/assets/192620/2809657/e8e98494-cd7a-11e3-901a-4f4cba17f4c8.png)