Move reuse last values for digitizing to attribute dialog.

[NathanW]

The attached patch moves [copies] the reuse last values check box into the attribute dialog when creating a new feature. I moved this here as you may want to remember the values for a couple of features then turn it off, create some different features, and then turn it back on again.

Having it in the attribute dialog makes it a bit easier to selectively choose when you want to remember values for the next time.