setup.py: added psutil dependency
tox.ini: install dominator[full] for tests
Container: added "doors" property
fixed command docstrings
"containers" command group renamed to "container"
"files" command group renamed to "file"
"images" command group renamed to "image"
"ships" command group renamed to "ship"
"volumes" command group renamed to "volume"
"doors" command group renamed to "door"
"image push" command separated from "image build"