Adding flow.js as a thirdparty dependency
Client side to accept drag drop and folder selection

WIP for attachments api

WIP2 getting id but not storing files in gridfs
Working api for imagefiles and attachments
Merge branch 'dev/dj-multi-image-upload'

* dev/dj-multi-image-upload:
  Working api for imagefiles and attachments
  Client side to accept drag drop and folder selection
  Adding flow.js as a thirdparty dependency