Feature request: Provide another way to interface with o.expr instead of o.expr.codebox

[alexlipscomb]

I think that the o.expr.codebox UI object is incredibly powerful, but some of the limitations are preventing me from using it more frequently. Issues such as not being able to edit the contents of the codebox while locked, not being able to save/read files, not being able to dynamically set the expression, etc. are all sorely missed features in my patches. I was thinking that instead of adding this functionality into o.expr.codebox, maybe it would be smarter to extract the expression evaluations into a separate object, allowing for messages to set the expression and for the user to handle file saving themselves.

Thank you very much!