Drag cursors

  - Use the grab/grabbing cursors instead of pointer
  - Only draggable widgets use a special cursor
update safe urls based on https://www.djangoproject.com/weblog/2014/may/14/security-releases-issued/
Updated quickstart to cover south migrations with easy_thumbnails
Fix widgy_mezzanine preview for Mezzanine==3.1.2

With the introduction of mezzanine.pages.context_processors.page, there
was a change in how PageMiddleware and the page view interact which
broke the PreviewView and HandleFormView in widgy_mezzanine.  This
commit fixes the problem in a way that works for both pre- and
post-3.1.2 Mezzanine.
Added tests for the preview view bugfixes.
Cursors for tabs
Merge pull request #202 from zmetcalf/update_quickstart

Updated quickstart to cover south migrations with easy_thumbnails
Update Docs for using widgy on existing mezzanine
Merge pull request #197 from zmetcalf/mezz_to_widgy

Allow RichTextPage in the Admin
Added get_css_classes to the Content model.

The previous implementation of class_to_json wasn't calling css_classes
because you can't call property methods without an instance.  I added a
method get_css_classes which works on both instance and classes.  This
allows widget creators to set css_classes on their widgets and for that
to work in both to_json and class_to_json.
Button css_classes have changed.
Merge branch 'drag-cursor'
Merge pull request #201 from fusionbox/mezz312-preview

Fix widgy_mezzanine preview for Mezzanine==3.1.2
Merge pull request #203 from fusionbox/buttonWidget

Change Button's css_classes so that it doesn't confict so hard.