platformdependent: v3

v3 introduces an async ready state that can be used to delay things
until the dependent has actually completely initialized. in particular
the kde dependent needs to async load credentials out of kaccounts.
currently that is using a nested event loop and causes crashes. with the
new architecture we can propagate async readyness properly instead.

- basejob now delays doWork until ready state is reached
- providermanage also delays provider loading
- since valid providers only come out of the manager all providers are
also delayed accordingly