Before this change syncthingwidgets unconditionally included the header
from libsyncthing so it couldn't be used as stand-alone library if
libsyncthing was disabled.
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 external inotify tool is likely not used anymore. It makes sense to
keep the concept of supporting additional tools because it might be used
in the future again. So it seems best to give the additional launcher a
more generic name.
* Lazy initialize systemd interface and don't initialize it
at all if the unit name is empty
* Allow to supervise/control system-wide units in addition to
user units (see https://github.com/Martchus/syncthingtray/issues/61)
* Avoid redundant code
This is useful because sometimes the background color of the system
tray is dark but the overall system UI still uses a light theme.
For the Plasmoid this should never be the case, though. Hence the
extra settings are not available there.
Add new SyncthingLauncher class which lauches Syncthing
under the hood via external SyncthingProcess or using
libsyncthing.
Note: Launching via libsyncthing is still experimental.
