Fix URL errors when configuring extensions in the presence of SITE_ROOT

The extension framework used str.lstrip() to try to strip off the SITE_ROOT
from the admin URL root, but the problem with that is that lstrip takes in a
set of characters, not a string. If that set of characters included "a" and "d"
(for example, if SITE_ROOT is "/reviewboard/"), it would remove those
characters from the beginning of "admin/...".

Reviewed at https://reviews.reviewboard.org/r/4892/
Merge branch 'release-0.7.x'
Fix one more "except ..., e" spot.

Looks like I missed one in my earlier change. Trivial fix.
Fix hiding edit icons in inlineEditor.

The wrong CSS visibility value was being used to hide the edit icon. It
was set to 'hide', but should have been 'hidden'.
Merge branch 'release-0.7.x'