set up modal

[evanwill]

opening this for discussion!

features:

• metadata set up modal with form for changing metadata using demo, web, or local options
• reads metadata url from url query string
• when metadata is changed dev buttons appear to refresh or change
• when no metadata is configured, the set up modal appears
• adds "development-mode" option which allows you to turn off all these ^ features
• adds loading icon when first fetching metadata csv (not during other page loads, since that just seemed to add unnecessary flashing)

[evanwill]

when you test, comment out _config.yml metadata-csv value so you can see the set up modal pop up automatically.

also i replaced the featured image with an abstract non-collection item, since it made more sense to have something like that, rather than be blank featured image each time you change metadata.