define tokengetter for each provider

auth submodules are registered with initialized
check if auth.local is loaded before accessing registration route
check DB_URI before attempt to create db

oauth authorize callback to use absolute url, needed by Facebook

fix

The parameter names must not be converted to upper case before calling
context.invoke, because that works with the lowercase names.

Before this bugfix,, we had kw like this in the various setup_* functions:
{'DB_URI': 'sqlite:////tmp/wiki.db', 'db_uri': 'sqlite:////real/path.db'}
and whichever won was pretty much random (dict sort order)

Closes https://github.com/scragg0x/realms-wiki/issues/76