[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'