Move caption into asset edit form (#765).

Uncomment line in static/js/models.js to include caption in asset
editing form. Remove special-case code for editing captions
in-place.
Remove dependency on jeditable plugin (#765).

Update readme, builder template, and spec runner. Remove plugin
files.
Merge branch '765-edit-caption-behavior' of https://github.com/patternleaf/atlas
Filter stories in admin based on template status

Addresses #808