Fix the display of dashboard-like pages.

The dashboard-like pages (users page, All Review Requests, etc.) broke
with my recent dashboard display fix. They were appearing hidden. We now
only hide by default on the actual dashboard page.

Reviewed at https://reviews.reviewboard.org/r/6283/
Provide additional information for exception traceback e-mails.

This adds new middleware to provide information on the username and
e-mail address of the user who triggered the exception, if any. It also
logs the Local Site name, if one is set.

Reviewed at https://reviews.reviewboard.org/r/6278/
Add hostingsvcs.change_hostingserviceaccount perm to local-site admins.

On master, the unit tests for the remote repository resource are broken because
permission tests for the hostingsvcs.change_hostingserviceaccount permission
for local-site admins don't work. I'm not sure why this doesn't also break on
2.0.x, but either way this permission should be listed.

Testing done:
Ran unit tests.

Reviewed at https://reviews.reviewboard.org/r/6281/