Add toString() for UFAuthHandler
Correct type annotation
Cleaner handling of session/auth instantiation.

Also don't inject the currentUser, as the session won't have been init()'d
at that point, so EasyAuth will throw an error in get_currentUser()
Small fix for inline session middleware
Revert context injection on constructor.

Instead provide a workaround for ufTrace, ufLog, ufWarn and ufError so they
will work even before `context()` is set.