Have xcw and xcg just output their value

By simply outputting their value their output
can be used in a command more easily.
Ensure WORKING_CONTAINER and GOLDEN_CONTAINER values have content before using them
Add xcgc command

The xcgc command outputs the path to the WORKING_CONTAINER config file.
This can be easily used to cat or edit the file.
For example:
cat `xcgc`
emacs `xcgc`
Add xcm command

The xcm command is used to configure a container to mount
a host directory in the container's filesystem.