Begin implementing renaming of linked datasets.

This adds a renames parameter for linked files, mapping the names.

This needs to be handled for each datatype. Also change doImport to
put datasets into a dict, rather than directly into a document.

Also actually use encoding parameter for standard import.

Drop changesets for individual datasets.
Replace saveToFile for each data format with call to helper
Small simplification
Implement renaming for remainder of data formats.

Make all command line commands return list of import datasets and print when verbose.

Make doImport not have to pointlessly return list of datasets
Remove unused imports
Remove debugging
Fix HDF5 dialog after changes. Do not save empty dataset attributes.
Fix capture after changes
Move capture dialog to new style signals/slots
Add self test for renaming, update README, use doc.setData