[#106] Implement Traffic Statistics API

Closes #106 (closed)

This MR adds a new app of traffic_statistics with a single endpoint:

{base_url}/statistics/api/?start_date={dd-mm-yyy}&end_date={dd-mm-yyy}/

This endpoint will return the daily View, Comment, Download, and Like counts from the given date range in JSON format.

Sonarqube report here.