Child params

[jdranczewski]

When creating a Popup, it would be useful to have a way to automatically create child params that match specified parent params of the parent Piece. These should have the same kind of input, and play nicely with the getters and setters of the parent params.

This way, one could have a bunch of hidden params in a given Piece, and trivially create a Popup with additional settings which modifies the parent Piece's params.

• [x] Implement a way to create child param objects
• [x] Add a method to Popup that automatically creates child params given a list of names of the parent Piece's params to replicate
• [x] A similar system for actions would probably be nice too

[jdranczewski]

See https://github.com/jdranczewski/puzzlepiece/commit/d36ee774a8cce3d0a70afc48adbfd2f940ffac99 for initial implementation