Add Follow/Unfollow group button
Add tests for Follow/Unfollow group button
Add links to sidebar navigation

I added links to the pages that exist so far. I omitted the link to the
privacy section of the user profile because we cannot yet jump directly
to it.
Fix privacy link assertion
Add icon-lock class when toggling privacy settings

The design uses icons applied with CSS classes rather than toggling the
visibility of a separate lock element.
Merge pull request #196 from azavea/feature/jcw/add-main-nav-links

Add links to sidebar navigation
Merge pull request #198 from azavea/feature/jcw/add-lock-icon-to-privacy

Add icon-lock class when toggling privacy settings
Merge pull request #184 from kdeloach/topic/follow-unfollow-groups

Add ability to follow/unfollow groups
Show group detail breadcrumb link on edit page
Move group detail URL construction to model

- This property is idiomatic to Django
- Removes the need to add an additional context item
- The Django admin will create hyperlinks if this is defined
Correctly set group editability context var
Merge pull request #197 from azavea/feature/jcw/group-detail-link

Add group detail breadcrumb link to the top of group edit
Add allows_individual_mappers to Group

This commit also sets up a copy of the form on the group settings page
to allow setting this attribute, and hides the button to request
individual mapper status if the group does not allow it (or the person
viewing the group detail page is already an admin)