Remove the FolderDocuments model simplyfing the Folder model and related views
Use the auto_now_add option, removing the need to override the save method
Use auto_now_add
Explicit new checkout check, remove unused import
Update auto_now_add and auto_now for the documents app models
Use auto_now for the dynamic_search app
PEP8 cleanups
Use auto_now_add for the lock_manager app
Simplify code, remove import
Use auto_now_add in the bootstrap app model
Use auto_now_add in the history app
Add API endpoints to add and remove documents from folders
Simplify the API to attach or remove tags to a document