Expand functionality of New Image plugin

This implementation is an improvement over the previous 2d-only
plugin. It is not as fully functional as we want (i.e. adding and
removing axes dynamically). But it currently supports XYZCT and
can very easily be made to support more (with key code marked
with a TODO).
Update code to reflect API changes in NewImage plugin

Note that running the InvokeCommandTest plugin currently fails in
invokeFromJava() with an NPE.
In New Image persist all dimension dialog fields
Fix NPE bug caused when InvokeCommandTest plugin is run