Units metadata panel

Still a work in progress, but would like to know if I'm on the right trac...

In the Metadata Forms, I'm putting the Value in the field and the Unit in brackets (see screenshot). Units are displayed "as is" but probably need converting from CAPS to lowercase?

Also unsure if I need to do more Null checking.
I've just been picking attributes by using a couple of metadata-rich files, but it would be nice to have a complete list of all the places we've added units.

![screen shot 2014-11-25 at 00 19 30](https://cloud.githubusercontent.com/assets/900055/5175923/54e80732-7439-11e4-88c0-1160bbbdf751.png)