Remove the AuthWidget, have AuthJob open real browser instead

I've lately seen issues with Google claiming that the app of the
browser is not secure. As such it is safer to just use a real
web browser. It also means we can get rid of the awful webengine
dependency in KGAPI.

AS of now, the AuthJob will simply launch a browser, wait for user
to click through the authentication there and wait for the tokens
to be sent by the browser via a socket. Implementations are encouraged
to not launch the AuthJob silently as that might confuse users as to
what is happening, but instead do so upon a user action.