This allows to use the username as a placeholder in the config paths (Autotext, Gallery, etc)

Change-Id: I76434e980cd8ec8785a5587d0bc5fdd67dc42de2
Reviewed-on: https://gerrit.libreoffice.org/22901Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>