Fix initial state of "Download Diff" vs. "View Reviews"

The code to initially hide the "Download Diff" link for interdiffs got messed
up due to a merge-o, and the result is that it was hiding "View Reviews"
instead.

Reviewed at https://reviews.reviewboard.org/r/5592/
Fix a bunch of jshint errors, generalize tests.

This change fixes a bunch of errors found by jshint. Most of these are silly
things like missing semicolons. This also changes our use of 'public' to
always use string notation, so that we're not using a reserved word.

When I was running the js-tests, I found that different browsers used different
orders for attrs which had been added from javascript when calling .html().
This meant that several of our field tests broke when running in firefox. I've
changed this to test more generally instead of looking for specific html
strings.

Testing done: Ran js-tests.

Reviewed at https://reviews.reviewboard.org/r/5595/
Change _.super to _super.

"super" is a reserved word as of ES6. This makes jshint very unhappy. This
change fixes up all our call sites to call it "_super" instead. Once this is in
I'll push a trivial change to rb-extension-pack to update its use of _.super.

Testing done: Ran js-tests and jshint.

Reviewed at https://reviews.reviewboard.org/r/5600/
Split up _find_review_request to retrieve the ReviewRequest object, then check permissions.

Currently, `_find_review_request` retrieves the ReviewRequest object matching an
ID and checks permissions, returning `None` if the review request is not
accessible by the user. Splitting this up into two parts (retrieve the
ReviewRequest object first, then check for permissions) allows us to get a
ReviewRequest object in cases where permissions are not needed.

Testing Done:
- Manually checked that the review request details page shows up.
- Ran unit tests.

Reviewed at https://reviews.reviewboard.org/r/5603/
Merge branch 'release-2.0.x'