Make the label element optional for form fields.

Labels for form fields can be disabled by setting them to an empty string. Previously this would produce the intended result visually, but left an empty label element in the HTML. This change causes the element to only be inserted if a label value exists.
Added David Sanders to AUTHORS
Added mezzanine-admin-backup to apps in README.
Fix for uploading zip files to a homepage gallery
Fix login/logout redirects for sites with a URL prefix.
Update to latest bleach/html5lib and enable for Python 3.
Fix admin menu app/model sorting for Python 3.
Merge
README syntax fix
Bump version to 3.0.5
Update auto-generated changelog, docs, requirements.
Don't require specifying filebrowser urls separately in a project's urlconf.
pep8 fix
pep8 fix
import the user model from settings
Improved support for determining timezone with tzlocal lib.
Added Mezzanine powered sites to the README

It's been a long time since I've added anything =)
Update README.rst
Merge
New setting EMAIL_FAIL_SILENTLY for controlling the default fail_silently arg in sending email.