Aligned with vanilla midPoint container. Upgrade to midPoint version
4.8.3. Most of the configuration is dynamic, limiting the need of
building custom containers.

Beware! This is an incompatible change. The new connector has no support
for "old" object classes (AccountObjectClass, GroupObjectClass) and uses
a different name for "plain" groups (ri:CustomPlainGroupObjectClass ->
ri:Group). Also the name and uid attribute names has been changed to
ri:name and ri:uuid.

Obsolete midpoint-objects directory was renamed appropriately before
it's definitely deleted.

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

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.

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

Removed obsolete directories; merged others (namely, logging)
into midPoint/Grouper scenario.