[bug 1030532] Needs change comment now cleared.

When the box is unchecked and the form is submitted, the comment
is now cleared.
Merge pull request #2005 from dean/revision-persist-1030532

[bug 1030532] Needs change comment now cleared.
[bug 1006574] Top contributors infrastructure.
[bug 1006574] Implement initial UI for top contributors.

* Implemented the top contributors view and template
* Implemented the top contributors on the Community Hub landing page
[bug 1030348] Fixes issue with Topic selection Dropdown
[bug 971782] JS fix for data bucketing (weekly, monthly).

The bucketing implemented in Rickshaw does not like missing data
for any dates. It wants explicit 0s. This zero-fills all the
dates.
[bug 987337] Show topic descriptions on topic pages.
[bug 1032175] Update error message
[Bug 1031906] Update error message in users/forms.py
[bug 1001145] Track usage for canned responses
[bug 984007] Fix localization status on L10N dashboard
[bug 1019649] Add news section to community hub.
[bug 970214] Send a weekly "Ready for review" digest
[Bug 1033339] Fix latest_version in product view.

This is a partial revert of 64d896f1d7524a4b45648a10ee2d99988eb49e83
[bug 682235] Encourage kindness when asking questions
[bug 892871] Mobile user settings page
[bug 972850] Tag questions with FxOS device info
[bug 570433] Enable flagit for contributor forums
[bug 766394] Added migration for  migrations user.

This is the user we should use for data migrations when having
to assign owners/creators to new objects.
[bug 766394] Auto-generation for share links.

Share links for KB articles should now automatically generate
if the articles are in the correct categories. A cron job runs
every day at midnight as well to add share links where there should
have been some, but currently aren't.

Additionally, the bitly api key and username need to be entered in
settings.py for share links to generate.