FORGE-1953: Add command to get and set JVM system properties

This PR is intended to implement the feature request https://issues.jboss.org/browse/FORGE-1953.

The idea is to add a new command to get/set system properties.
Even though we can do it that way, I think it is a bit confusing to do all actions in a single command. We can combine the list and get actions into one command and leave the set action in a separate command as follows :
- system-property-get : list all properties
- system-property-get --propertyName foo : get value of foo property
- system-property-set --propertyName foo --propertyValue bar : set bar to property foo

George, Lincoln, what do you think about this definition?
I believe it is clearer from a user's point of view. But we can still combine all actions into a single command as George suggest, it would be killing 3 birds with 1 stone ;-)