_QLButton should be able to accept more arbitrary types

(Bug, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Functions
Summary: Currently, you can only pass Thing references into _QLButton, either as context or bound names. In principle, this should be generalized.
This fails because many useful PTypes don't have serialize() functions. For example, ParsedTextType can't do it.