Fix sending the current document by e-mail:
 - fix path to the installed senddoc executable
 - add missing exception for xdg-email
 - execute xdg-open and xdg-email unconfined

Change-Id: Ie7c5b112bd6c415036490e9f0f81063ca3ced5a1
Reviewed-on: https://gerrit.libreoffice.org/49614Reviewed-by: Rene Engelhard <rene@debian.org>
Tested-by: Jenkins <ci@libreoffice.org>