[SD-945] Moved base_schema to common and renamed it to metadata_schema
[SD-945] Extracted timestamp adding to a method in base class IngestService
[SD-945] Created superclass for all parsers and refactored existing parsers to point to new superclass
Merge branch 'SD-945'
[SD-945] Renamed parse to parser. Refactored metadata_schema from apps.common to apps.content
Merge
Merge branch 'master' of https://github.com/marwoodandrew/superdesk-server
Merge remote-tracking branch 'remotes/upstream/master'
Merge remote-tracking branch 'mayur/master'
Merge remote-tracking branch 'andrew/master'
fix(ingest): don't push `media_archive:created` event when ingesting
feat(unlock): add user id to unlock notification

in order to display who unlocked the item we need to add user id into
pushed notification.

SD-1002
fix(ingest): make use of _id so we can fetch it in realtime