Improve structure

[zaporylie]

I decided to simplify repo structure and combine all Dockerfiles for single PHP branch into one folder.

Pros:

• less folders - less mess
• shared config files (drupal-*.ini) - huge benefit!

Cons:

• when you build image manually you have to provide filename for Dockerfile, ex. docker build -f ./5.6/Dockerfile-cli -t local/php:5.6-cli ./5.6
• for all the cli images we have to first set defaults and then override it with cli-specific overrides

IMHO the pros are over the cons and that PR should be merged into master.

[zaporylie]

Calling @slashrsm: I would appreciate your review!

https://github.com/drupal-docker/php/tree/improve-structure

[slashrsm]

Looks good to me.