* Update documentation and provide an example compose file for postgres

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

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

* Added missing env in the example compose file

 * FIxed missing modification from past commit

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

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

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

[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