[Misc] Use a better (more specific) tomcat image tag so that if tomcat changes the jdk version for tag "9", we won't be affected

[Misc] Remove my name and email now that the module is in the XWiki GitHub Organization and this maintained by the XWiki Committers

* Revert the MySQL upgrade because of issues for 12.10.x and 13.2.x branches

* Also update the MySQL driver from 8.0.22 to 8.0.23

* Verify the MySQL driver download to avoid man in the middle attacks

* And switch to AdoptOpenJDK 8.x for XWiki 10.x (since XWiki 10.x doesn't support Java 11)

* 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)

* More progress, still not working

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

 XDOCKER-10: Cannot change database name
* Add leftover that was forgotten

* Implement a simple Gradle build to generate the various versions/variants.

[Misc] Improve doc (was committed as part of "XDOCKER-13: Add an image tag for XWiki 9.0 and publish on dockerhub" on the 9.x branch)

[Misc] Fix wrong VOLUME location issue introduced when I refactored the code to depend on the tomcat image instead of on debian jesse directly...

[Misc] Apply best practices as reported by yosifkit on https://github.com/docker-library/official-images/pull/2563#issuecomment-276541490
* Removed the not needed sh files
* Allow passing parameters to catalina.sh from the docker command line
* Removed unnecessary apt upgrade + unncessary --force-yes option
* Verify sha of xwiki war to make sure the right WAR is downloaded and avoid man in the middle attacks
* Simplify the sed expression and do it in one step
* Remove unnecessary EXPOSE (done by the tomcat image)
* Install the MySQL JDBC driver using apt-get (libmysql-java package) instead of getting it directly from upstream

[Misc] Add missing license headers + apply docker best practice for consistency (see https://github.com/docker-library/official-images#consistency)

* Fix typo from previous commit
* Remove the need for sudo and the need to execute as tomcat user
* Removed CATALINA_HOME and CATALINA_BASE from setenv.sh since they're not taken into account and copy setevn.sh to the right place
* Nano wasn't needed either (was a leftover)

[Misc] Spread ENV variables so that they are placed just before where they are used so that we can use Docker's build cache as aggressively as possible. Suggestion from Tianon Gravi.