SequenceRule refactoring.

1. Rename SequenceRule->IllegalSequenceRule for consistency with other
   rules that have negative semantics.
2. Rename SequenceData->IllegalSequenceData for consistency.
3. Add IllegalSequence type to describe sequences (e.g. differing case,
   variant forms).
4. Create EnIllegalSequenceData enum with common sequences (alpha, numeric,
   keyboard).
I would call this class 'Sequence', there's nothing inherently illegal about it. It may have other uses outside of the IllegalSequenceRule.
I don't find the term original or variant to be meaningful and I don't think providing these as Strings versus char[][] provides any more clarity.