Optional envelope trailers

The following X12 EDI envelope trailers are now optional when converting JEDI 2.0 to EDI:

IEA GE SE LE

When these trailers are not included in the input JEDI, they are automatically generated based on the contents of the corresponding header and envelope. This simplifies the generation of EDI for users, as they can avoid potentially toilsome tasks such as counting the number of segments nested within a transaction set.