Trello 49: FEAT: Data Display Widget

Trello 49: FEAT: Data Display Widget

Draft of API and technical documentation available in the wiki at http://wiki.datadryad.org/Data_Display_Widget_API

The code in this PR has been merged into datadryad:dryad-dev, deployed on dev, and tested minimally for widget display and functionality. This commit also pulls the banner widget API into the same dspace module. That functionality was also confirmed to be worked as expected on dev.

The integration tests for the display widget are not being run as part of the Travis-CI build, as documented here http://wiki.datadryad.org/Testing#Headless_Selenium_tests . There are unit tests in the widget code that run, but none that run currently that test the front-end/browser functionality.