KVerifiableData: Validate data by type, constraint or dependency

This class is meant to validate data sets, like for instance submitted form input values, according to several types of criteria:

* Data items may be set as required or optional.
* Types of verification constraints include: minLength, maxLength, minValue, maxValue, moreThan, lessThan.
* Can specify and verify by type: string, integer, float, boolean, date, time.
* Data items can be arrays or comma-separated lists.
* Can specify dependencies between items; e.g. A must be less than B, or sizeof(A) must be equal to sizeof(B).