Send email when closing review requests

Optionally send emails when closing review requests. Add a flag in the Email
settings page that will allow for sending emails when a review request is closed
(Submitted/Discarded).

Files Changed:
reviewboard/admin/forms.py
+ Added Boolean to store the value of "mail_send_review_close_mail" in settings

reviewboard/notifications/email.py
+ Added callback method for review_request_closed signal

reviewboard/templates/notifications/review_request_email.html
reviewboard/templates/notifications/review_request_email.txt
+ Added code to display the "Status" of the review request when it's closed
  before the "Description" section.

Tests:
+ Added test for review request closing
+ Modified other review related tests to fix counts or expected results

Testing done: Added test for this feature and ran all tests. Verified in UI.

Fixes bug 422
Reviewed at http://reviews.reviewboard.org/r/3707/
Add a capability to indicate support for Perforce moved files.

1.7.2 introduced moved file support for Perforce, but there wasn't a
good way for RBTools to really detect this that retained compatibility
with previous versions of Review Board. The reason is that we relied
upon the existing general diffs.moved_files capability, causing RBTools
to generate diffs for older releases that ended up being incompatible.

This introduces a scmtools.perforce.moved_files cap that can be used
instead. 1.7.3 will be the minimum version of Review Board that will
support moved files for Perforce with RBTools.
Add a new BaseResource model that will be used by all API models.

The BaseResource model provides all the common functionality for dealing
with requests and parsing results, ensuring a model is ready to use (has
its data fetched) before we do anything with it, and being able to
ensure it's created before using it. These models have a concept of a
parent resource that they're under (for example, a diff being under a
review draft).

This change just introduces this model and a suite of unit tests for it.
We'll move over to this in subsequent commits.
Merge branch 'release-1.7.x'