Update to the latest jQuery version.

Review Request #1122 — Created March 12, 2018 and updated — Latest diff uploaded

Review Board
This change moves us over to the latest versions of jQuery and
jquery.form. This was relatively painless, with only a few changes being

- `$(func)` or `$(document).ready(func)` now always invoke their callbacks
  asynchronously, even when the DOM is already loaded. This interfered
  with one of the PageManager unit tests.
- Our autocomplete fork had some manual checks for old Opera browsers which
  are obsolete, and didn't work now that `$.browser` is gone.
- `$.fn.load` used to do two things (one loaded stuff, the other
  attached to the load event) and now only does one. We had one place
  that was using the removed behavior (the event), which has been
  changed to `$.fn.on`.
- The naming scheme for the widget in element data changed in jQuery UI, so
  that the old data name "rbautocomplete" is now "uiRbautocomplete".
- `$.fn.andSelf` has been removed, in favor of `$.fn.addBack` (which
  always existed, and did exactly the same thing).

Testing done:
- Audited the codebase for anything that would have been problematic with
  deprecations and removals.
- Ran js-tests.
- Smoke tested the UI.

Reviewed at https://reviews.reviewboard.org/r/9714/