Register rewrite Update.

The main things in this patch is I think the model is working correctly now,
you can add, change and delete same currency transactions along with different
currencies asking for exchange rates and also share accounts.

Other changes:
- use the default GTK_TREE_VIEW sort mechanism.
- Added cut, copy & paste
- Added right-click context menu.

Author: Robert Fewell Register rewrite Update.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@22815 57a11ea4-9604-0410-9ed3-97b8803252fd