Owner trust levels considered valid keys:
  Marginal
  Full
  Ultimate

Owner trust levels considered invalid keys:
  Unkown
  Undefined
  Never

Change-Id: I7338b587acfd105ca24e40b45960cea8d2c04ded
Reviewed-on: https://gerrit.libreoffice.org/39952Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
Tested-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>