Modifications in order to set multiple payment informations in one singl...

I made some to your project in order to have multiple Payment Informations in one single SepaDebitTransfer.
* The type of Sequence isn't in the "SepaDebitTransfer" anymore, but in "SepaDebitTransferTransaction".
* When the code write the XML, he loops through the types of Sequences that he can handle ("FRST", "RCUR", "FNAL" and "OOFF") and extract the SepaDebitTransferTransaction to insert in the XML.
* A SepaSequenceTypeUtils has been added in order to translate an Enum value to a valid string.
* The Test classes have been updated in order to reflect those changes.