gpkit models needs a setup script

[whoburg]

Need a simple setup.py so that users can install the package and use it in other applications.

First, we need to decide what the package name is:
gpkitmodels?
gpkm?
gpkmodels?

We'll move all the models into a folder of that name.

[bqpd]

I favor gpkitmodels

[pgkirsch]

It seems this issue should have been closed by #61