Minor tidyups in the list_tiddlers part of htmlserialization

This is still a big mess. So many variables are being set and
then passed to the template. User visible changes include:

* when listing non-search results, the URIs are not fully qualified
  with host etc
* the search template uses the default title block from base.html
Clean up openid challenger slightly

Mainly to limit the number of variables created and make
the flow a bit more clear.

I believe this commit probably marks my first use of try: except: else
Take indexer out of config.

'indexer' (used by filters and recipes) has proven to not be all
that useful with more optimized stores and tiddlyweb in general.