Break out utility functions from main package

[jakeboone02]

• Create a new package @react-querybuilder/util with all utility functions (and default settings/classes/etc?). util should not require react.
• Modify ts package to officially export two sets of types, one with react and one without. util package should use the latter.

Initially, react-querybuilder should re-export everything from the util package to minimize disruption to users. We can think about removing them in a subsequent major version.

Might think about tackling this and #396 together.