Add an integration for Asana.

Review Request #9363 — Created Nov. 11, 2017 and submitted — Latest diff uploaded


This change adds a new integration for linking to Asana tasks from
review requests. This consists of a few pieces: the integration config
which connects to a specific Asana workspace, and a review request field
which allows people to search for and link to multiple tasks.

The UI is currently fully functional, but at a later date I'd like to
make it look a bit more like the related object selector used in the
admin UI, with the search box shown above the list of selected items
(instead of swapping out the entire UI for what looks more like "tags"
inside the selectize widget).

  • Tested success and error conditions within the integration config UI.
  • Added a bunch of tasks and verified that everything loaded correctly.
  • Saved the field in a variety of states.