Fix for connected story links failing (#487).

Add a click handler for connected story links to render the connected
story when no Backbone router is present (ie, when we're in an
iframe).
Show asset thumbnails in viewer connected story section (#610).

Includes template addition and some styling.
Merge branch '610-connected-story-thumbnails' of https://github.com/patternleaf/atlas into 610-connected-story-thumbnails
Use featured_asset tag instead of calling render_featured_asset (#610).

Allows for requesting appropriate size rather than pulling a full-size
image and then scaling down via CSS.
Merge pull request #686 from patternleaf/610-connected-story-thumbnails

Adds display of connected story thumbnails in the "Connected Stories" section
of the story viewer.