* Also propagated the upgrade of the MariaDB connector from the previous commit to the various environments

XDOCKER-225: Allow customizing the JDBC connexion parameters + add "allowPublicKeyRetrieval=true" by default for MySQL
XDOCKER-285: Change default MySQL/MariaDB charset + collation to utf8mb4

  * Missing update of docker-compose so that the build don't put back
    12.1-alpine

* Also update the compose files

* More progress, still not working. I have an issue with "jdbc:postgresql://replacecontainer:5432/replacedatabase" not working and generating " Caused by: java.net.UnknownHostException: xwiki-postgres-db"
* Added ascii art in Dockerfile
* Renamed containers so that we can run several xwiki images on the same machine without conflict

* Use a better name for the property (thanks to Tianon)

* Prepare the field by generifying the templates/build and docker files

'Creating network "xwikimysqltomcat_bridge" with driver "bridge"'

[Misc] Go back to the previous setup which was better and I've found a way to make DockerHub happy with it.

[Misc] Since we may want to generate different images of xwiki in the future (with different dbs, different servlet containers, etc), move all current data into a xwiki-mysql-tomcat directory.

[Misc] Big overhaul to separate image-time setup from runtime configuration + added some license headers

[Misc] Improved README + give a name to the xwiki-data volume + add LICENSE + improved .gitignore file