Added a CommandWithTerm Class

Added new CommandWithTerm Class similar to the CommandWithMeta Class.
Designed to reusable for different object types. Currently this is draft and I am still testing it. Just wonder if I was on the right track with this solution. Feedback is requested. I will write tests when I know that I am on the right track. 

Related #1379
Again, the CommandWithMeta. 
https://github.com/wp-cli/wp-cli/blob/master/php/WP_CLI/CommandWithMeta.php#L113

Doesn't it make it harder to test as we don't control what is outputted. If WordPress changes for it's output or if different language is loaded, the message would be different.