Update docker images to modify mysql configuration

Dockerfiles are updated with two key changes:
- use streamline's official images as a base
- replace two files related to mysql configuration

A README.md file is added to the docker folder which details the changes, but
the key difference is to limit binary logs to only the `streamline` database.
This prevents additional system databases from being included, which the
database sync tools do not (yet) support.

An unrelated bugfix corrects the docker-compose image tag, specifying 'latest'
instead of a previously hard-coded version.

docker/Dockerfile.streamline-emr.amd64

@@ -1 +1,4 @@
-FROM conrad96/streamline:2.0
+FROM streamlinehealth/streamline:signalytic
+
+COPY my.cnf /etc/mysql/my.cnf
+COPY mysql-init.sh /var/www/html/.docker/mysql/mysql-init.sh