Reinstate map delete function.
Fixes #1510
Fix backend store.
Refs #1510
Group all backend data functions into one class.
Retrieve empty hash block.
Fixes #1607
Save hash maps like blocks - based on their hash.
Refs #1169
Avoid duplicates in missing hashes reports.
Fix blocker.
Fix hash map PUT conflict.
Update documentation.
Move hashfiler to backends folder.
More modular backend.
Start of modular backend (not working yet).