and use the users preferred initials for impress annotations

i.e. the ones entered in the tools->options

and save and load those to/from odf similarly to
what we do for writer annotation initials

Change-Id: Iadc0e994bfaf58632ce25b8f7cdc737580ee97bc
Reviewed-on: https://gerrit.libreoffice.org/22143Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>