Add draft 2.0 release notes.

This has everything from the 2.0 beta 1, beta 2, beta 3, RC 1, and RC 2
releases, plus the changes that have gone in since RC 2, minus the changes and
bugfixes that have been backported to 1.7.x, and minus any fixes from later
prereleases for features introduced in earlier prereleases.

Testing done:
* Built HTML and read through it.
* Did some fancy-pants grepping to check for backported bugs.

Reviewed at https://reviews.reviewboard.org/r/5717/
Sandboxing NavigationBarHook get_entries

Added unit tests to test sandboxing

Testing Done:
* Unit testing, added to test suites in reviewboard/extensions/tests.py
* Unit testing with and without the sandboxing

Reviewed at https://reviews.reviewboard.org/r/5708/
Require the latest Django 1.4.11 security release.

This fixes a number of security issues. Most importantly to us, a bug in
reverse() that could lead to importing unexpected modules, if the
attacker knows which modules are on the server.

See https://www.djangoproject.com/weblog/2014/apr/21/security/
Release Review Board 1.7.25.
Merge branch 'release-1.7.x' into release-2.0.x
Merge branch 'release-2.0.x'
Fix using the wrong directive in the 1.7.25 release notes.

This was using :cmd:, which should have been :command:.
Merge branch 'release-1.7.x' into release-2.0.x
Merge branch 'release-2.0.x'
Beanstalk post-receive web hook

This is a Beanstalk post-receive hook that will automatically close review
requests as "submitted" after a push. To determine which review requests should
be closed, it scans through each commit's commit message for the following
strings (case-insensitive): "Reviewed at <reviewboard_url>/r/<id>" or "Review
request #<id>".

This is what the JSON payload looks like:
http://support.beanstalkapp.com/customer/portal/articles/75753-trigger-a-url-on-commit-with-web-hooks

Testing Done:
Test carried out on git and svn repos.

1) Push with the review request id in the commit message. Review request
   closed.
2) Push without a review request id in the commit message. (Review request
   closed based on the commit_id for git and error looged for svn)
3) Push with non existent review request id. (Error: Review request does not
   exist)
4) Push with review id in the message that is already submitted. (logged a
   warning: request id already submitted.)
5) Push with review id in the message that has been marked as discarded.
   (review request marked as submitted.)

Reviewed at https://reviews.reviewboard.org/r/5698/