This adds a few layers of functionality:
* Support for preemptive actions that run before data
is loaded into the table (saving on API calls).
* "Update" actions that fetch new data for specific rows.
* Automatic AJAX polling for rows which are in an "unknown" state.
The table/action changes were accomplished without breaking any existing tests.
Also includes unit tests to verify the new behavior.
Lastly, includes a big chunk of new docs to begin flashing out topic guides
and examples for working with Horizon beyond just an API reference.
Change-Id: Ifd15919066825d7269bbe4efcb4d51b8ed19baed
95970b701c