WIP: Change tab URL to be restful.

I will re-visit this PR after the item.py refactoring is done.

Here are some caveats:
1) Creating and saving static tabs is still done through the generic save_item and create_item view methods. Changing the tabs to use the tabs URL for this seemed like a pretty big change, especially since we have a desire to revamp the static tabs page to allow more control over all the bas.

2) Reordering of the tabs IS done through the tabs URL, but it is perhaps a little weird (in the fact that it just sends a list of IDs). I documented the expected payload, but I can imagine this will change in the future.

3) No Jasmine tests exist for the tabs coffee file. I didn't feel like creating these tests (especially given the desire to revamp the UI), but I did extend the existing Selenium tests (which covered addition and deletion of static tabs) to cover reordering. Therefore, the code I changed is covered by automated tests.