Adjust to FloraWeb dropping support for paging through search results

This uses the register/lexicon pages instead of paging through search results which is much simpler but also yields only 5.500 instead of 30.000 search names.

I think some of the difference between 30.000 and 5.500 is due to synonyms which we would have pruned during duplicate removal in any case, so this in effect just much less wasted work which would be good for everybody. But systematically combing through the "Stammbamm" section shows that there are indeed some newer entries which are not listed in the register/lexicon pages.

I think we should either contact the FloraWeb team to ask whether this intentional or can be fixed or whether they would prefer for us using a different API altogether, or we just wait this out as FloraWeb is continuously reworked and the register/lexicon pages are also based on the older XSQL approach so will probably see a PHP rewrite eventually as well.