Minor tweaks to initial public release

These changes were simply to get the repo into a slighly better state for external technical review. The only changes since the initial commit are:

I modified the README.md file to reflect the the actual name of the project (Geomag-IMP, not G-IMP)
I changed the name of the IPython Notebook in the test folder
I added some functional tests and demonstration cells to the IPython Notebook.

usgs / geomag-imp