Remove unneeded call to Handlebars.compile
Factor template handling into base view

Factor template handling in Backbone views into a base view,
``storybase.views.HandlebarsTemplateView``.  This is implemented through
``storybase.views.HandlebarsTemplateMixin`` which allows the view handling
capabilities to be mixed in to objects other than views.

This approach makes template handling more consistent and makes it easier
to swap out template engines if we ever decide to abandon Handlebars.

``HandlebarsTemplateView`` takes a ``templateSource`` property which is
either a string containing the template markup, an object with keys
mapping to template strings, or a function returning a template string or
hash of template strings.  When specifying an object, the main template
is identified with a key of ``__main``.

A compiled version of the main template is assigned to ``this.template``.
If an object was provided for ``templateSource``, a particular compiled
template can be retrieved using ``this.getTemplate(key)``.

Addresses #707
Inherit events from ViewerApp

Subclasses of ``ViewerApp`` should inherit their events from ``ViewerApp``.
Otherwise, things like the table of contents toggling gets clobbered.

Closes #709
Updated changelog

Addresses #709
Merge branch 'hotfix-709-toc_toggle' into develop
Wrap Backbone modules in self-executing functions

Wrap Backbone modules in self-executing, anonymous functions.

This allows us to more safely use local variables in each module reducing
the repetition of things like ``storybase.builder.views``.

This commit also removes the dependency on Namespace.js. It included support
for things like asynchronous downloading of modules which we're not using.
Instead, we'll just create the namespaces explictly.

Addressess #710
Move Backbone app globals out of separate namespace

There wasn't any real good reason to have globals attached to
storybase.(viewer||explorer||builder).globals.  Instead, just attach them
to storybase.(viewer||explorer||builder)
Remove StoryHeader view

This was commented out and likely won't return.  Just remove it.  We can
use git to recover it if need be.
Remove console log statements

Remove console log statements in the builder. End users don't care about
them and they were cluttering up the console in testing. Now that the
builder is more stable, they're less needed.
Make viewer header not be position:fixed (#684).

Also make header box-sizing: box-border so horizontal scrollbar isn't
required.
Fix indentation in viewer code (#715).

Just an indentation fix (and one comment). No semantic changes.
Fix indentation in viewer code (#715).

Just an indentation fix (and one comment). No semantic changes.
Prevent wrapping in header-right menu (#702).

Prevents long usernames from wonkifying layout.
Merge pull request #718 from patternleaf/715-modal-viewer-toc

715 modal viewer toc
Update changelog

Addresses #715
Merge branch '715-modal-viewer-toc' of https://github.com/patternleaf/atlas into patternleaf-715-modal-viewer-toc

Conflicts:
	static/js/viewer/views.js
Update changelog
Merge pull request #720 from patternleaf/702-long-usernames-in-header

Prevent wrapping in header-right menu (#702).
Update changelog
Avoid race condition when updating index

Signal handlers are used to update the search index when SectionAsset
instances are deleted.  This works fine when they are deleted
explicitly, but causes a problem when they are deleted via the cascade
when the related Section is deleted.  When the section is deleted, the
story can't be fetched via ``instance.section.story``.  To work around
this, story a reference to the story in a ``pre_delete`` signal handler
so its available in the ``post_delete`` signal handler.

Addresses #723