Preserve ENV variables for SSH client

Currently when you ssh to host you will not see ENV variables set. This was mentioned earlier in #54 and solution is tested.

Additional rationale: currently you can't see docker link ENV variables inside ssh, so you need to load this file every time you connect to container. I would say that expected behavior is to preserve them in services that are provided at default (cron/ssh)
Make container_envoriments.sh and .json readable by other users

Prevents bug when loading env variables on non-root user login.
Add docker_env group and make container_environment scripts group-readable
Update readme
Merge pull request #84 from imanel/patch-1

Preserve ENV variables for SSH client