Improve QIF import

[dospuntos]

The QIF import script could use some improvements:

• Import account name if available (currently defaults to "Bank account #"
• Import date correctly (currently all transactions are set to date of import) - done with 53dec60
• Add some error checking, e.g. check if below each ^ delimiter, there's a date, amount, payee or category
• The QIF format does not support currencies, a warning to review account currencies could be useful.

It would also be nice to show some stats after the import, like how many accounts and transactions where imported.