Add: role docker-mysql

ansible-galaxy init roles/docker-myssql
Rem: useless files
Mod: rename docker-myssql into docker-mysql
Mod: README, meta and define the license
Mod: the playbook docker-mysql installs mysql \o/
Add: install mysql on all servers
Merge branch 'devel/role-docker-mysql'
Mod: standardize some stuff
Merge branch 'devel/standardize-readme'