* Use a process group / job object via Boost.Process to be able to
terminate sub processes as well
* Do not try to stop the process gracefully under Windows by posting
WM_CLOSE because this has no effect on Syncthing anyways
* See https://github.com/Martchus/syncthingtray/issues/94
Add new SyncthingLauncher class which lauches Syncthing
under the hood via external SyncthingProcess or using
libsyncthing.
Note: Launching via libsyncthing is still experimental.
First step of refactoring compution of high-level
notifications to prevent code duplication for compution
of "disconnected" and "sync complete" events.