Refactor Transaction Type

[Techworker]

The Techworker\IOTA\Type\Transaction class has way too much logic embedded. We will need to refactor most parts of it, especially the parse and __toString methods contain a whole bunch of logic to either interprete or create a transaction trytes string.

Together with that, we should think about something like lazy parsing. The parsing process itself is not complicated but really slow, so initializing a Transaction instance with existing Trytes takes much too long.