Move logic for services autostart from klauncher to ksmserver

Summary:
Currently ksmserver sends DBus calls to klauncher to autostart services.

This patch brings all autostarting into the ksmserver process, putting
all autostart code together, and improving Plasma/Frameworks separation
(change requested by David Faure) with the long term goal of removing
this from klauncher; with a longer term goal of maybe even killing
klauncher.

We don't get two things autostarting as without ksmserver sending the
signals, klauncher does nothing.

Autostart.cpp code is copied verbatim so there's no breakage.

Test Plan: Logged in, got plasma and krunner and so on.

Reviewers: Plasma, graesslin

Reviewed By: Plasma, graesslin

Subscribers: mart, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D2544