Provide methods to set different textEngines via builder interface

[rus4j]

Description

For now Numbify can be built using various TextEngine. Like:

Numbify de = new Numbify(
    new German(Currency.NUMBER),
    new CombinedText(
        new IntText(new SolidText()),            // solid text for int part
        new DecimalText(new DigitByDigitText())  // digitByDigit text for decimal part
    )
);

It should be possible to do the same thing through NumbifyBuilder.

Requirements

• add digitByDigitInt(), solidInt(), customIntTextEngine(TextEngine textEngine) to set specific text engine for int part of the number
• add digitByDigitDecimal() (already exists, fixed that), solidDecimal(), customDecimalTextEngine(TextEngine textEngine) to set specific text engine for decimal part.
• Tests