QIF import: match target account

[tuxlifan]

Probably going to be easier once @brownnrl's #26 Import Plugins are done, but until then:

How would I go about implementing automatic selection of the target account during QIF import?

The condition being that only one account will be specified (at the beginning of the file), e.g. using:

!Account
NChecking
TBank
^

which I could catch in parse_account_line() in core/loader/qif.py.

I tried to mess around with self.target_account but got nowhere and am not sure how it fits together...

Thanks!