gnome-gmail: Support quiet setting of pref mailer

This obviates the need for setOOmailer (if OpenOffice is better
behaved).
Remove the last vestiges of GTK2

This means replacing setOOmailer with a mode of gnome-gmail, and
otherwise pulling LibreOffice hacks. The gconf schemas are gone,
as are the GNOME2 email handler xml file.
Fixes to support setup.py install

Add the glade file to the install, and have gnome-gmail do a bit
of looking for it across prefixes.
Update po files to latest code

msgmerge -U
Update version to v1.9 and log Changelog entry
gnome-gmail: Replace IMAP with the GMail API
gnome-gmail: Remove 'user cancelled' notification