[GNC] Adding security during import

[Fred Tydeman]

When I import a QIF file that contains stocks that GnuCash does not know
about, I get a screen to provide details about Tradable commodities.

It would be nice if there were a button at the bottom to advance to the
next security (in addition to the existing advance to the next screen ==
QIF import)

I realize I can click on Back after clicking on Next, to get back to the
Tradable commodities screen to do other stocks (when I clicked on Next by
mistake).