Add support for OFX/QFX

[theflanman]

OFX and it's derivatives like QFX are common standards which contain much more metadata about transactions than (most) csv files do, which are highly dependent on what the company decided to export. Support for OFX/QFX transactions would substantially reduce the adoption barrier of this tool.

OFX docs https://financialdataexchange.org/FDX/About/OFX-Work-Group.aspx