Also with other minor enhancements.

1. demo/plain -> demo/simple
2. updated README.MD

The container is now built directly from the root directory.
Even the simplest composition was moved to demo/plain.

It was not easy to build two Docker images in TIER Jenkinsfile
(using docker/util). It seems that tier/mariadb:mariadb10 is OK to be
used with midPoint without any customizations, so we use it.

This was for testing the logging requirement concerning UTC timestamps.

This is to avoid Shibboleth problems when opening
http://localhost/grouper instead of https://localhost/grouper.

Building is now more straightforward and better documented.
To quickly see timezone problems we have set Central timezone
for various containers.

This is a rework/update of the original "Grouper-midPoint" demo.
It is a work in progress. Do not use yet.

Now the default port is derived from the database type.
Also, PostgreSQL demo was cleaned up.

These containers are used to demonstrate Shibboleth-based SSO
capabilities of TIER midPoint Docker container. They are NOT to
be used in "midPoint-Grouper" demo.