Adding messageclass to enable multilingual exceptions and messages and better cross-referencing.
Enhancing ZCX_EXCEL to have a substitute for non-classbased "message .... raising"
and to enable unittests that are independant of logonlanguage when checking exceptions raised this way.
git-svn-id: https://subversion.assembla.com/svn/abap2xlsx/trunk@427 b7d68dce-7c3c-4a99-8ce0-9ea847f5d049
