Introduce new localisable abstraction - INumberToWordsConverter

Move English, Arabic and Farsi converters to a separate strategies.
EnglishNumberToWordsConverter - promote units and tens maps to a static fields to reduce allocations.
ArabicNumberToWordsConverter - promote arrays to fields to reduce allocations
FarsiNumberToWordsConverter - promote arrays to fields to reduce allocations
Move ToOrdinalWords method to INumberToWordsConverter
EnglishNumberToWordsConverter - refactoring
Introduce DefaultNumberToWordsConverter which just returns string representation of a number
minor cleanup
restructuring Localisation folder a bit
Merge branch 'NumberToWordsConverter'
added NumberToWordsConverters to release notes