Bug 715184 - Bill or Invoice; a new Bill gives a new Invoice

Fixes the labelling in the bill or voucher windows and the new dialog.
It doesn't fix the bug, but is related to it.

Note to translators:  Introduces four new strings
"Voucher Information", "Bill Information", "Bill", "Voucher",

modified:   src/business/business-gnome/dialog-invoice.c
modified:   src/business/business-gnome/gnc-plugin-page-invoice.c

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23458 57a11ea4-9604-0410-9ed3-97b8803252fd