Call getSelectedFiles instead of getFiles+adapt behavior so it deals
with an array of files with their full path

Change-Id: I21b6c32dea85460461925a9b44dac195d79b7eac
Reviewed-on: https://gerrit.libreoffice.org/18714Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>