Remove redefinition of inherited property

NOTE: This should not be merged before this has been:
https://github.com/genome/UR/pull/43
Move ColorMixin from Command to Utility

Since it does not inherit from Command it belongs someplace else.
Make doc clearer
Add Genome::Command::WithColor

This is a Command::V2 so its attributes can 'is_param'.  This is needed
in order to have an attribute show up in the help or be accepted as a
command-line argument.
Update test data for Define-docs.t
Merge pull request #185 from davidlmorton/color

Remove redefinition of inherited property