Keast Spinal Connectivity Model Tests

[jrmartin]

• [x] Download the Keast Spinal Connectivity Model. https://raw.githubusercontent.com/open-physiology/open-physiology-viewer/master/test/data/keastSpinalTest.json
• [x] Go to http://open-physiology-viewer.surge.sh/
• [x] Load too-map.json using the 'Load Model' button.
• [x] Load keastSpinalTest.json Connectivity Model, with 'Merge with Model' button
• [x] The panel with Groups should be populated. The tests for this Model should be to toggle the Groups on and off.

[ddelpiano]

input required from @enicolasgomez on desiderata for the testing strategy since this model keeps changing.