Add initial base implementation of API
Add Offer model and refactor Place and BaseModel
Add JSON-LD serialising and model improvements

Note: deserialization still TODO
Freeze dependencies in requirements.txt
Add (de)serializing support for camelCased JSON fields

Django and database have convention to name fields in undes_score. Schema.org's
fields are camelCased -> conversion is needed.
Add plenty of model changes, serializing modifications and comments
Enable creator and editor fields in few models
Enable parent relation in Place
Add basic API access for persons
Add admin and initial serialization for Person
Add contained_in relation to Place
Add model mods and small template customisation
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.