openSAFETY: Add datafield for preload

 - Block Up-/Download will be removed from the protocol
   It has never been implemented => no impact
 - Preload will be added in future versions of the
   openSAFETY specification
 - Better definition of SSDO ACMD sets to ensure correct
   protocol dissection
 - Use TFS.h t/f strings where applicable, remaining
   strings are referenced directly from specification

Change-Id: I9c809098938333c914e1f8ba67d100b994fd33f4
Reviewed-on: https://code.wireshark.org/review/2647
Reviewed-by: Roland Knall <rknall@gmail.com>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>