Make the mangement of data file parsers more friendly and modular

[stadelmanma]

Currently it would be very awkward to add more parsers for an end user because not only do you have to edit the helpers file but you also have to edit the ledger#edit view. Ideally I could add a 'parsers' directory to my application and add them all there. New parsers would need to be a subclass of the DefaultFormat. For the ledger#edit view I could just pull all of the subclasses and the base class itself instead of hard coding them.

A rename of Format to Parser might also be good.