This is very preliminary support, and is likely to still fail for many
cases - even those with nominal support. Most transaction splits end up
being filed under 'imbalanced' accounts instead of something that makes
more sense.
This is the more sensible location for it, since we import things on a
per-account basis - so there can be more than one remote ID associated
with a transaction, and the splits are the per-account portion of
transactions anyway.
