Removed stale home page listing code.

I removed the Django CMS plugin code because they're no longer used and I
think that the template tag approach that we've taken lately is nice
because it's more CMS agnostic.

I removed some of the helper functions for rendering the plugin output since
they're also no longer used and that logic seems better encapsulated in
template tags.

Addresses #198
Explore page: story titles should be left justified. (#576)
First pass at homepage banner

This is a first pass at the homepage banner implementation.  It doesn't
implement any kind of background generation or caching and currently only
selects stories randomly.

Still to do:

* Background rendering and caching
* Other strategies for selecting stories
* Registration pattern for different story selection strategies and method
  on the registry for selecting the different strategies or a random
  strategy.

Addresses #198
Wire in story links.

Forgot to replace the dummy links when I did my first pass of the
homepage banner feature in eb3719e02a4e90fe804df96633f289e0dc17c86c

Addresses #198
Merge pull request #620 from patternleaf/576-left-justified-titles

Explore page: story titles should be left justified. (#576)
Update changelog.

Update changelog to mention fix for #576 that @patternleaf implemented
in 418a38e21951b8251aaface0756d65ebeefbe262
Merge branch 'hotfix-622-scale_viewer_image_borders' into develop

Conflicts:
	README.rst
More robust search for django-admin.py

The apply_djang_patches script called from ci_before_script.sh started
failing in the Travis CI build.  The reason was that django-admin.py
wasn't being found.  Try executing the script directly, instead of being
called with ``bash`` from ci_before_script.sh and try explicitly activating
the virtualenv from ``apply_django_patches``.

Addresses #626
Merge branch 'hotfix-623-catch_js_errors' into develop

Conflicts:
	README.rst
Merge branch 'develop' into 198-homepage_banner
Registration pattern for banner implementations

Provide a registration pattern for different banner implementations.

The ``banner`` template tag now takes ``banner_id`` as an argument to
select a particular banner implementation and keyword arguments that
are passed to the individual implementations.

If ``banner_id`` isn't specified, a random banner is selected.

Addresses #198
Banner implementation selecting stories by topic

Addresses #198
Debugging for Travis build

Addresses #630
Point Travis Jetty at correct location of JDK

Addresses #630
Merge branch 'develop' into 198-homepage_banner
Added a ga_campaign_params template tag

Added a template tag for generating the query parameters for a Google
Analytics Custom campaign.

I'll need this to support analytics and A/B testing with the banner.

In order to test this, I refined the SettingsChangingTestCase.
Clean up use of SettingsChangingTestCase

Use the set_setting method instead of this sloppy setting changing
set up.

Also, the inheritance order was whack, even though it didn't really matter
in this case.
Merge branch 'hotfix-634-turn_off_error_popup' into develop

Conflicts:
	README.rst
Add Google Analytics campaign parameters

Add Google Analytics campaign parameters to banner links.

Addresses #198.
Merge remote-tracking branch 'origin/develop' into 198-homepage_banner