Pass scripted properties through validation/normalization code.

This commit modifies the validation and normalization code to ignore script
directives for the `required`, `range`, `length`, `default`, and `repeat`
properties. This doesn't modify `lib/input.js` to actually execute script
directives; that wfunctionality will follow shortly in a second commit.

Add test cases for the validation/normalization script directive pass-through.
Merge branch 'master' of https://github.com/medic/medic-forms