- simplify VCLExceptionSignal_impl
- drop "minor" part of error code, nobody passes it in, and nobody
checks it
- rename Display to UserInterface, to prevent -Werror=shadow

Change-Id: I503fd8a50ded30d59c30fb388796f6b1a0c058de
Reviewed-on: https://gerrit.libreoffice.org/24892Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>