Added new requirements and built base structure for API.

Installed djangorestframework and django-filter for API.
Setup new API app for handling API requests.
Setup basic list and detail views for call and participant objects.
Built two basic serializer classes with references on FK serializing.
Setup urls.py for API app - no actual URL endpoints set yet.
Enabled admin interface and setup templates directory and matching settings directory.
Finished basic API implementation.
Merge branch 'feature/api' into develop