Add support for the other MWS report types

[laconc]

ReportType enumeration

As can be seen in the link above, MWS provides numerous reports, although some won't be of value to this project, such as _GET_XML_ALL_ORDERS_DATA_BY_ORDER_DATE_ , which is data that we're already receiving through a different report type. The only ones currently included are:

_GET_FLAT_FILE_ALL_ORDERS_DATA_BY_ORDER_DATE_
_GET_FBA_FULFILLMENT_CUSTOMER_RETURNS_DATA_

This issue will be kept open to track report types until all the useful ones are added.