Remove orange button from legal agreement view

The form validation (and eventual event triggering) is now triggered
when the checkboxes are checked rather than when the form is submitted.

Addresses #515.
Add numbers to the publish view steps

Add numbers to the publish view steps. I did this by making each
sub-view's element a ``li``.  I had to do a bit of CSS trickery to style
the ordered list numbers to match the headings.
http://www.456bereastreet.com/archive/201105/styling_ordered_list_numbers/
was very helpful with this.

I still need to test this under IE.

Addresses #515
Use LESS variables for publish step number styles

This is a tweak to the changes made in 2a8bcadaa92e1417c09d52e3053383b12115f325
that uses LESS variables to make the publish step numbers match the
header styles instead of hard-coding values.  This should make the code
more future proof.

I added a ``@styled-header-family`` variable to variables.less and also
use this variable to set the font in the ``.styled-header`` mixin in
base.less.

Addresses #515
Merge branch 'develop' into 515-publish_cleanup
Merge branch 'develop' into 515-publish_cleanup
Refactor publish step views

There was too much logic in the publish step templates and too much
logic related to toggling various elements based on publication status
in PublishView.  I broke most of the UI elements such as the publish
button, the to-do list and the view/publish buttons into their own views
and broke out common utility methods and initialization to a base view
class.

Addresses #515
Tests for PublishButtonView and PublishTodoView

Addresses #515
Merge branch 'develop' into 515-publish_cleanup
Tests for PublishedButtonsView

Addresses #515
Merge branch 'develop' into 515-publish_cleanup
Make get_default_img_url_choices a class method

get_default_img_url_choices and get_default_img_url don't touch the
instance object, and should return the same value for all instances, so
they can be a class method.  Doing this lets me bootstrap a value into,
say, a Backbone view without having a model instance.
Upgrade Backbone and Underscore

Upgrade Backbone and Underscore libraries to most recent version.

Backbone goes to version 0.9.10 and Underscore goes to version 1.4.3.

This is mostly because I wanted to start binding to events on models and
collections, when possible, instead of the event bus.  As of Backbone 0.9.9,
there are now listenTo and stopListening methods on Events, which make
binding event callbacks a little cleaner.

Note that in this version of Backbone, the Backbone object extends
Backbone.Events so it can be used as a global event bus.  Doing this might
make the code less verbose in the future.

I had to change the Asset model validation test to reflect the way that
validation doesn't automatically happen on Model.set and that invalid data
sends the "invalid" event rather than "error".
Checkpoint commit for new featured asset views

Addresses #515
Merge branch 'develop' into 515-publish_cleanup
Rebuild CSS

I forgot to rebuild CSS in c0cf382265c5620e1d0be26180526980a7ee55f9

Addresses #515
Update styling of asset type selection. Display normal full-range asset selection, but if there is a pre-selecet asset type, show only that asset as available. Includes a comparison operator handlebars helper. Addresses #381.
Simplify builder asset type selection template and view implementations. Suggested by @ghing. Addresses #381.
Remove unneeded compare handlebars helper.
Fix preview of connected stories.

The "Preview" link in the story builder was linking to the normal story
viewer for connected stories.  This is problematic first because the
section titles aren't hidden and second because users will never view
a connected story in the story viewer.  Instead, they show up in the viewer
of the seed story.

To fix this, I had to change a few things on the back end.  I needed to
include draft connected stories in the template context for story viewer.
I did this by overriding the ``get_context_data`` method of
``StoryViewerView`` and passing a ``connected_stories`` context variable
that contains the filtered connected stories list instead of calling the
story instances ``connected_stories`` method from the template.

I updated ``Story.connected_stories`` to take arguments that would cause
it to return either only published connected stories or published connected
stories and drafts for the logged-in user.

To activate the different connected stories behavior, I added a
``preview`` url route that passes a ``preview`` keyword argument to
``StoryBuilderView``.

The preview URL is then passed to the Backbone views by ``StoryBuilderView``
as a template string (so the builder can parameterize it with the story
ID to handle the case when a new story is initally saved).

Finally, I updated the story viewer Backbone views to properly display a
connected story when accessed directly by it's hash-based URL in the
browser's location bar (rather than being accesed through clicking links
in the view).

Addresses #601.
Merge branch 'hotfix-601-connected_story_section_titles' into develop