Added support for mapping commands, command factories, and output of
commands to their corresponding version relative to a supplied reference
location. 
An intermediate support is added by implementing MappableCommand,
MappableCommandFactory, or MappableOutput for adding such mapping logic
for, respectively, command, command factories, and output of commands.

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>