Add generic parameter to pass Docker container options

[annybs]

At the moment we make some Docker options available via 'proxy' arguments like --network etc.

Supporting a growing number of possible container options for various environments may become cumbersome so we should look at the possibility of generic inputs, keeping in mind that Edge CLI does not proxy Docker CLI but rather the Docker Engine API, so something like --docker-args '--memory 100mb' may not be especially simple.

In any event, if we add the ability to specify container options arbitrarily, we will have much more flexibility to configure systems.

This solution would supersede #133 and other existing container options.

To be explored.