Allow subclasses of HttpRequestHandler to implement other methods than OPTION and POST.

Remove remaining part of the core (+ generalize the tests library).

I can haz recursion

Conflicts:
	ppp_core/config.py

Export the Config class so modules can use it instead of reimplementing it.

Fix wikidata integration

Update to doc

Use ppp_datamodel.communication.* objects for interacted with the request handler.