Add the ability to customize the server name (+ several improvements)

[smourph]

This PR integrates some changes from:

• Fixed problem with permission on edit /etc/hosts #96 (thanks @zomberg)
• Add opcache, xsl and intl, share 3306 port of db container and adapt logs shipping for sf3  #92 (thanks @PyRowMan)
• Use nginx official image #91 (thanks @elaman)
• Added intl PHP extension to PHP container #79 (thanks @ksowa)

Changelog (by commits) :

• code(customization): general docker improvements
  • minimize RUN number (perf)
  • add container names
  • add ports forwarding
  • upgrade debian 8 to 9 (and to a lighter version)
  • upgrade PHP 7.1 to 7.2
  • fix permission with /etc/hosts
• feat(customization): add the capability to customize the server name
  • add an environment variable to customize the server name (SYMFONY_NGINX_HOST)
  • use the official nginx image: lighter + works withour Dockerfile
• code(customization): improve symfony integration
  • install intl (sf dependency)
  • install opcache (perf)
  • install the symfony application to init projects
  • adapt log configs to work with sf3