Add check for lookup jd import default displayname

Ok, firstly this naming code is hideous but it is trying to deal with the data it is getting. Basically, Google requires givenName and surname field separately so we try to guess what to use from display_name, cn (aka registered_name), given_name (aka first_name) and surname provided by Lookup.

This could be completely re-written but I've gone for a quick fix of not blindly using display name if it is different from registered name. It now checks whether the display name is the same as would be generated by default by Lookup's jackdaw import and skips to trying given and surname next.

Closes: #39 (closed)