OmeroCpp: Split omero-client into omero-ice

All slice-generated sources are build into a separate omero-ice
library.  omero-client contains the remainder of the sources
and depends on this library.  This reduces the symbol count
sufficiently to allow omero-client to link on Windows platforms
without triggering any link errors.
OmeroCpp: Correct _EXPORTS defines for separate libraries
blitz: Remove old C++ logic