First round of Nikon ND2 fixes

This should fix the problems described in http://trac.openmicroscopy.org.uk/ome/ticket/11998 and http://trac.openmicroscopy.org.uk/ome/ticket/10939.

For ticket 11998, the relevant files are in QA 7906 (apache_repo/7906 or data_repo/from_skyking/nd2/qa-7906).  I would expect all of them to open and/or import with no error, and be single planes with 3 channels.

For ticket 10939, the relevant file is in data_repo/from_skyking/nd2/cameron.  I would expect this to have 8 Z sections and 4 channels.

For this and subsequent .nd2 PRs, imports can also be verified by checking what the file looks like in Nikon's software: http://www.nikoninstruments.com/Products/Software/NIS-Elements-Viewer/.