So far the backend libraries' include paths were relative within this
repository. This means the header files could not be used at their
installed location.
This change replaces them with "<>" includes to fix that problem and adds
a new include directory so building everything at once still works.
With this change it should be easier to actually split some parts into
another repository if this one would become too big.
The following uses of QCC1/PlasmaComponents2 remain:
```
…/DetailView.qml:import org.kde.plasma.components 2.0 as PlasmaComponents // for Menu and MenuItem
…/DevicesPage.qml:import org.kde.plasma.components 2.0 as PlasmaComponents // for Menu and MenuItem
…/DirectoriesPage.qml:import org.kde.plasma.components 2.0 as PlasmaComponents // for Menu and MenuItem
…/DownloadsPage.qml:import org.kde.plasma.components 2.0 as PlasmaComponents // for Menu and MenuItem
…/FullRepresentation.qml:import org.kde.plasma.components 2.0 as PlasmaComponents // for vertical TabBar
…/RecentChangesPage.qml:import org.kde.plasma.components 2.0 as PlasmaComponents // for Menu and MenuItem
…/TopLevelView.qml:import org.kde.plasma.components 2.0 as PlasmaComponents // for Highlight and DialogStatus.Closed (used with Menu and MenuItem)
```
* Syncthing Tray can be considered stable enough
* Syncthing itself also made a 1.… release some time ago
* The backend libraries still do *not* provide a stable API, see section
"Using backend libraries" in README.md
* See https://github.com/Martchus/syncthingtray/issues/59
* QCoreApplication::aboutToQuit() does not work reliably but terminating
only at the end of the session is a common use-case for the tray
application. So workaround the problem by saving the settings
immediately.
* The plasmoid already does this anyways.
* This allows running C++ GUI code (as provided by this
repository) and Syncthing itself in the same process.
* It basically seems to work. I can now run a Syncthing
instance within the interactive C++ shell 'cling' :-)
* Syncthing and its assets are built within the usual
CMake build process but disabled by default because still
experimental. To enable the build, add '-DNO_LIBSYNCTHING=OFF'
to CMake arguments.
* The Syncthing checkout with customized exports lives
in the Git submodule under
'libsyncthing/go/src/github.com/syncthing/syncthing'.
