Created generating maskers; revised date handling in all date maskers.

Renamed mask(T[]) in AbstractDictionaryMasker to maskArray to prevent
name collisions with mask(T).

Replaced Period with ReadablePeriod and DateTime with ReadableDateTime
for method arguments in concerned date masker classes.

Created and implemented AbstractGenerateMasker as well as inheriting
classes GenerateRandomDecimalMasker, GenerateRandomIntegerDecimalMasker
and GenerateRandomDateMasker.