WIP: Medium latency EM_COINC specific circulars upon PyGRB and X-pipeline coincidences

I wrote the template needed in jinja2 to follow the needed wording (https://wiki.ligo.org/pub/Bursts/MessageToMouPartners/Circulars_final_draft). There is 3 new txt files (em_coinc_subject.txt , em_coinc_circular.txt, em_coinc_authors.txt) filed with what we need.

We need now to fetch the information from graceDB and put it in the template as in the init.py compose function do. I'am not sure yet if we want to build a new code containing the "compose-like" function or if we just need to put a flag on the existing one.