Add naive context implementation, model changes and util file
Fix property name in GeoInfo
Add provider field to Event
Add improved context creation supporting multiple models if needed

TODO: real dynamic creation based on fields, not on static definition
Add support for json-ld media type and dynamic context creation
Add support for JSON-LD parsing
Data extraction part of Matko importer.
Working parent event detection for matko.
Temporary parent saving database.
Model changes.

Added a data source and made same_as logic more dynamic.
Added a fixture for data sources and yaml dependency.
Added a URL field to store event www page (translatable).
Modifications to importer to reflect model fields.

Parent/child importing logic is functional for matko.