docker: remove dev image, update documentation

Relates to https://github.com/shaarli/Shaarli/issues/843

Changed:
- Update Docker image list
- Update Docker documentation structure

Removed:
- Delete Dockerfile and resources for the `dev` image
- Cleanup `doc/` resources

Signed-off-by: VirtualTam <virtualtam@flibidi.net>

doc/md/docker/shaarli-images.md

@@ -7,7 +7,6 @@ repository.
 ### Available image tags
 - `latest`: master branch (tarball release)
 - `stable`: stable branch (tarball release)
-- `dev`: master branch (Git clone)
 
 All images rely on:
 - [Debian 8 Jessie](https://hub.docker.com/_/debian/)