Embed sample data cab file into main msi file

 * This solves these issues:
     1) Web download packages failed to collect sample data
     2) Silent install ignores all external cab files, because
        the SourceDir property is set too late when no UI used
     3) Running the installer for a second time and selecting "modify"
        does not bring the sample data back into the feature tree
        if the cab file wasn't there on the first run but was
        subsequently added.

Change-Id: I7192e42668f3ce4e02bf5a1c7faec130f936b2af