`fenicsproject run <image> <command>` issues

[Jack Hale]

Currently:

docker run -ti quay.io/fenicsproject/stable "ls -l"

works, but:

fenicsproject run stable "ls -l"

does not.

Furthermore, one cannot use the default container to run a one-shot command, e.g.:

fenicsproject run python

This requires some logic to detect the meaning of the second and third arguments to the script.

[Jack Hale]

First two issues fixed in commit 0e1d4cd

[Jack Hale]

Not going to fix third issue, others resolved.