fixes bug 908821 - Create admin UI for graphics adapter signature summary

r? @rhelmer (the django bits) and @selenamarie (the DB bits)

So, this introduces a new piece of Admin UI and middleware endpoint to go with it. 
Here's a 
![screenshot](https://f.cloud.github.com/assets/26739/2176373/fc56ea8e-95d1-11e3-9e2e-784ff7e70aa7.png) showing what the Admin UI looks like. 

It is also exposed in the public API but note that I set the cache to `0` on the model because I don't want any of this to be cached. If you make an update, you might want to check that it really got saved. 

![Screenshot showing it in the public API](https://f.cloud.github.com/assets/26739/2176386/39a5a772-95d2-11e3-814d-a2b5b2e66caf.png)

I'll try to highlight some areas of the code that are interesting and worth reviewing.