Add "latest" tag
(not needed for Jenkins but for standalone building and testing)
Use standard tier/mariadb instead of custom one
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.
Add building of midpoint-mariadb
...and added slack notifications as well.
Add first version of Jenkinsfile