Fix diacritics comparison for tags

Previously, if a tag with diacritics was added to an item with the same
tag without diacritics or vice versa, the item would be listed as
changed but the new tag wouldn't be added.
Compare note text to sanitized version when saving

This fixes a problem where an unchanged uploaded note that differed from
the sanitized version would be changed without any visible content
changes. Uploaded note text is now compared to the sanitized version.
(The same thing would happen if the sanitization process changed to
produce different output, though.)
Show 400 instead of 500 for unknown collection when adding item
Show the JSON when an assertxxxForObject() assertion fails