#411 Rename SerialTitle classes

[nils-herrmann]

No description provided.

[Michael-E-Rose]

Most importantly, we need dummy classes with the old names: these trigger a deprecation warning for the next major update and still import the new class.

[Michael-E-Rose]

Two more changes to the docstring please.

Could you please also add Sphinx redirects from the old pages to the new documentation using sphinx-reredirects? That extension is currently not used, so don't forget to add it to the requirements.txt and conf.py.