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).
Merge pull request #685 from patternleaf/487-browser-history-in-iframe-viewer

Fix for connected story links failing (#487).
Validate ``context`` parameter

As @patternleaf said, it's not a good idea to blindly accept user input.
This makes sure the ``context`` querystring parameter is in a list of
acceptable values and defaults to ``normal`` if no querystring parameter
is present or if the value is invalid.

Addresses #487
Bump version for #487 fix