Huge update: Adds bootstrap loader

All that's needed to load the photowall (having already loaded jQuery)
is to add a single div/section/whatever with the class
"photowall-container" and a data-layout tag of the layout json file,
followed by a script tag that sources "bootstrap.js".

Should be able to work with multiple photowall containers.
Allows for default template paths
Adds lightbox handlers to new format

Handlers placed on anchors with class "lb".
Also boostrapper takes a "local: true" option which, if set, will
grab files locally instead of from s3.
CSS is linked automagically now
Removes underscore dependency
Changes to builder and json structure

Removed "seed" endpoint, moved its functionality to index and test.

Builder:
  Changes "skip" checkbox to "show" checkbox
  Nests image data under "tiles" in json object
Makes all urls use https
A meta tag denotes use of local content over s3
Adjusts highlighting of tiles on mobile
Adds ability to load multiple grids on the same page
Fixes lightbox bug related to async template loading
Removes unused pages/assets
Adds comments for documentation
Fixes error with comparison math in sorting
Fixes builder using new config format
Adds embed code to copy/paste into entry
Corrects wrong bootstrap.js address
Adds another css override for the grid
Wraps embed code to not mess up mobile preview
Sizes mobile layout to match m.huffpost.com sizes