Embed widget height attribute needs 'px'

Addresses #529
Merge branch 'master' into develop

Conflicts:
	README.rst
Use ChromeDriver for in-browser testing

Firefox is broken right now and more Floodlight users use Chrome anyway,
according to analytics.
Pause a bit to allow story to auto-save
Clean up integration tests for storybase_story app

These tests were written against the wireframe theme so some of the
tests were failing against the current theme.
Clean up in-browser and integration tests

Many of the tests were broken since the theme for the different detail
pages was added.  Some of the tests that reflect functionality that is no
longer part of Storybase, such as asset detail pages, were removed.
Merge branch 'develop' into 433-homepage-redesign
Merge remote-tracking branch 'eric/433-homepage-redesign' into 433-homepage-redesign
Show item type in featured item list

List the type of item (Story, News or Project) for items shown in the
featured box on the homepage.

I also cleaned up the line height and margins of the item titles.

Closes #575
Wire in latest stories, projects and organizations

On the homepage, wire in latest stories, projects and organizations lists
at the bottom of the homepage template.

I created 3 new template tags to do this: latest_stories,
latest_organizations and latest_projects.

The heavy lifting is done by storybase.utils.latest_context and the
storybase/latest_objects.html template.

I chose 100px for the thumbnail width, because that's the narrowest
thumbnail size offered by Flickr, our most frequent oEmbed provider. To
accomodate this, I added 100px-wide default images as well.

Closes #575, Addresses #433
Run apt-get update before Travis install
Only bind file upload callback for image assets

SectionAssetEditView.processForm was binding the image uploading handler
for all asset types, not just images.  This is wrong, so I added a guard
to check for the existance of an 'image' field on the form.  This seemed
more appropriate than checking the model type.