Initial revision

Summary:
This service adds a log entry to a log JSON document. That will allow to serve
an up-to-date all.json file pending a more robust microservice (see rSERVERSLOG).

Test Plan:
Unit tests provided for the Log class.

Furthermore, a test client in TCL has been prepared to test also the adder code.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1060