SPARK-2143 [WEB UI] Add Spark version to UI footer

I took a very basic stab at adding the Spark version number to the UI header / footer. This is the simplest place I could think to stick it without getting into the CSS much, and this is how it looks:

![screen shot 2014-11-21 at 22 58 40](https://cloud.githubusercontent.com/assets/822522/5151133/2ff0522c-71d2-11e4-9814-e630f7f80f71.png)

Thoughts? I think it's nice to have in the UI but might need to look a little different.