styling helper that supports composite styles and caching

Summarized in the 'Styling' section in the README.md file. I'm pushing this out for review... it would need tests, and improved documentation, but I wanted to see if this is helpful to others.
This one is actually native to FXForms, it's there by default. In fact, this is how all styling/properties are passed in. But, agreed, it shouldn't be advertised and should not be the published way to style cells.