handle editing richtext block html source in a react-bootstrap modal
jsxhint
Merge pull request #297 from ENCODE-DCC/1501-html-source-editor

handle editing richtext block html source in a react-bootstrap modal
* 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