Deactivated both NullMarker and EmptyMarker for Excel

These must be checked by program code, not by loading routine, as 
EMPTY would lead to empty string, which would later on be detected as
NULL.
Adjust test for new behaviour
Service Handler Proxy Bugfixes
Better handling for setSystemConnector()
Merge pull request #19 from falbrech-hsdg/quickfixes

Quickfixes