Future of common_params and smartvars

So I have gotten some feedback that people like params, as smartvars
are too puppet class specific, and seem too much like parameterized
classes without actually being parameterized classes.

Thinking going forward we probably want to replace smartvars with
parameterized classes, and have params map to to heira variables. We
may also want to extend common_params, such that we can change the
scoping, as a configurable option, since Heira supports that.