Improved scheduled publishing interface.

-  There is an easy way to publish immediately (most common)
-  Added datepickers
-  Popups are now iframes that are isolated from surrounding page
Improved VersionCommit.__unicode__ representation.
remove ckeditor samples directory
Delete confirmation improvements

  - Change the confirmation message to include display_name: 'Are you
    sure you want to delete this section?'
  - Highlight the widgets you will be deleting with the `deleting` CSS
    class, so you can double check that you have the right one.
Fixed bug with rerendering a widget with a shelf.
Support for non-nullable WidgyFields

WidgyForms didn't work with them previously, because of how they handle
unsaved instances.

Also changes the default values for null, blank, and on_delete back to
their normal Django values. This might cause backwards-compatibility
problems, be careful.
Fixed deletion of direct default children.
Add a widgy.admin.js to keep the fancybox code

Also adds a loading spinner while the iframe is loading.
Merge branch 'improved_committing'

* improved_committing:
  Add a widgy.admin.js to keep the fancybox code
  Improved VersionCommit.__unicode__ representation.
  Improved scheduled publishing interface.
Fixed showActivity bug.

The code that calls showActivity/hideActivity accessed a jQuery
reference that doesn't have fancybox.  We need to close over a jQuery
value that does have the fancybox object.
deleted item highlight
rounded corner cutoff fix
Fun Fact: The internet is comprised mostly of cats
for tables with an edit option on each table row, the edit button is now displayed, reduced, and alongside the 'delete row' button
unsafe HTML widget icon
form styles for top-node editors
Make qs argument optional in PatchUrlconfMiddleware.get_urlconf

signalhandlers.patch_url_conf calls get_urlconf with a single argument.
Make FormSuccesHandler draggable

It's awkward to be able to drop the success handler anywhere, but
not be able to move it aftewards.
Preserve submit-button data in popup forms

If we disable the submit button in the submit handler, the browser won't
submit its value. We need this value to determine which button was
pressed.
Add get_action_links to Widgy owners

Models with WidgyFields should define a get_action_links method. It
takes a root_node and returns a list of links. This is used for preview
links.

  - Removes the dependency in core on widgy_mezzanine for preview links
  - Removes the VersionCommitAdmin.get_commit_name and
    get_commit_preview_url methods.
  - Removes an attempt at making forms.WidgyField work for non-model
    forms. We'll revisit this when it comes up.
  - Adds preview and diff links for every owner of a VersionTracker.