Add django-reset to dependencies.

We still use 'manage.py reset' in a few cases, and 'manage.py flush' is not an
equivalent replacement. This change pulls in the 'django-reset' package as an
optional dependency, which forward-ports this management command.

Testing done:
Ran './reviewboard/manage.py --help' and saw the reset commands.

Reviewed at https://reviews.reviewboard.org/r/6104/
Release Review Board 2.0.3.
Merge branch 'release-2.0.x'
Bump to 2.0.4 dev.
Fix the recaptcha registration URL.

Apparently google moved the registration page for recaptcha and didn't keep the
old URL functional. Trivial fix.

Fixes bug 3471.
Merge branch 'release-1.7.x' into release-2.0.x
Merge branch 'release-2.0.x'