Overload existing methods to accept NormalizationFunction (new interface added in 0.14)

[CodesAway]

For example, DiffHelper has several methods. Also, the diff logic (for Myers / Patience) itself needs to be updated.

[CodesAway]

Ensure null safe, so if pass null that won't apply any normalization. Don't throw NullPointerException (add unit tests).

Can add static helper method to NormalizationFunction interface

• Use firstNonNull helper method
• Use passed NormalizationFunction if not null
• Otherwise, use BEXNormalizationFunction.NO_NORMALIZATION_FUNCTION