* FIxed missing modification from past commit

XDOCKER-11: Stop using Docker link feature (legacy/deprecated)
XDOCKER-12: xwiki image is not laucnhed as a deamonbut as interactive
XDOCKER-10: Cannot change database name

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

[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)

http://jira.xwiki.org/browse/XDOCKER-11

[Misc] Fix typo in docker-entrypoint.sh that prevented using a custom mysql user name + Removed unnecessary env variable at runtime

[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] Fix sample docker-compose example for using xwiki now that xwiki has an official image on dockerhub

[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.

Dockerfile optimisations (docker image size)

RUN chown -R tomcat8:tomcat8 /var/lib/tomcat8 directive is extremely costly, adding a layers "changing" only the owner 230MB of data, thus adding 230 MB needlesly

Removing a few layers to correct this

Gained