Fixed package info for tifffile extension

It was installing the compiled C-code as a root package in the
site-packages directory. The tifffile module still worked because it
used alternative Python code when there was an import error.
Fixed problem with renaming root nodes

The name was not always updated in the shell dictionary
Fixed handling of new nodes

The previous change assumed that the node existed in the shell when
using the NXtree add function.
Rationalized handling of errors

Exceptions for menu commands now trigger a warning dialog using the new
report_error function. Before, exceptions might only appear in the
console.
Added a new copyfile function to NXFile

This utilizes h5py.copy for copying duplicating files. Also fixed a
problem when using a dtype of 'char' (used for historical reasons in
the Add menu).