Register rewrite Update, this adds the trading accounts option with some other changes.

This update adds the trading accounts option. Also included is a fix for the way the model is loaded and changes the way it the view gets refreshed. There are also some minor changes to transaction confirmation. Two new files have been added and some functions moved to these with more to follow.
Author: Robert Fewell

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@22920 57a11ea4-9604-0410-9ed3-97b8803252fd