Backbone infrastructure for Vega plugin.

* Added all needed view classes, javascript, and HTML templates

* Plugin only renders a "Vega" section when the item metadata contains a "lyra"
  field.

* No content is rendered yet - this will require injecting a vega javascript
  block, retrieving the actual file contents, and then carrying out the steps to
  actually render what is in the file, handling errors appropriately.
Got vega vis actually working
Merge pull request #190 from ronichoudhury/vega-client-plugin

Vega client plugin