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
Let's change this to `<taxonomy>...` and require one or more taxonomies to be supplied. This would mirror the behavior of `wp term list`:

```
salty-wordpress ➜  wordpress-trunk.dev  wp term list
usage: wp term list <taxonomy>... [--<field>=<value>] [--field=<field>] [--fields=<fields>] [--format=<format>]
```