Add Number Schema

[joeyhoer]

I don't see a number option in the schema docs. It would be nice to have a number schema (perhaps with min/max limits) for user settings; I believe the current solution would be to either use a text field or a dropdown.

Example: I was considering adding an option to BigClock for "lightness" (effectively "brightness"; using the same color functions added here), so that lightness could be user configurable. Currently, there is a color value coded for "Dark Red", and I was thinking that it would be best to remove that value, and allow the user to select "lightness" independent of the color. (An even better option would be a more robust color picker schema, but a number schema could still be useful!)

[joeyhoer]

I moved this issue to the community repo.