* add image collection
* refactor attachment component out of Document in biosample.js
* add item block view
image add/edit form (including upload widget)
handle drag/drop file upload
improve validation of uploaded attachments
don't render actions when item is embedded in a block; display caption; don't re-fetch item blocks if uuid didn't change
refactor antibody attachment rendering to use the Attachment component
add fallback block edit form for blocks we don't have specific forms for yet
Merge pull request #296 from ENCODE-DCC/1498-image-collection

Add image collection and edit form
Merge remote-tracking branch 'origin/master' into 1504-upload-s3
Allow specification of multiple subpath_segments
Basic file download.