Error handling in profile view
[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 766394] Added column for share links.

max_length is 24 characters, which should cover the url lengths
as they grow for years to come.
[bug 766394] Added migration for kb share links.
[bug 766394] Share links now add to database.

They are not generated yet, but there is a base set up for putting
them in the database if the box is checked.
[bug 766394] Generate share links for KB articles.

Share links are generated via bit.lys API, and the configuration
for accessing that API can modified in settings.py.
[bug 766394] Added show/hide share link option.

Added migrations, form element, and now share_links are auto-generated
for each new KB article, but you can choose to hide or show them.
[bug 766394] Fixed styling for share link button.
[bug 766394] Fixed error for showing share link.