Support containers specific arguments

This version of dockeri supports the use of command line arguments destined to the container (internal environment) itself.

Docker containers working as apps may accept command line arguments: when docker run ... <image> whatever comes after the name of the <image> docker forwards into the container environment.

X11 support for MacOS

Fix bug regarding X11 server permission that was vanishing between environment calls.

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Interface for Interactive and Dettached-mode containers

This first release provides support for both interactive and dettached-mode containers.
Dockeri is stable in both Python 2 and Python 3.

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Python 2/3 and HEASoft included

This release-candidate supports Python 3 environment.
For convenience, the HEASoft container is included in the preset config file.

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