Features:
+* Add AddUser= setting to unit files, similar to DynamicUser=1 which however
+ creates a static, persistent user rather than a dynamic, transient user. We
+ can leverage code from sysusers.d for this.
+
+* add some optional flag to ReadWritePaths= and friends, that has the effect
+ that we create the dir in question when the service is started. Example:
+
+ ReadWritePaths=:/var/lib/foobar
+
* sort generated hwdb files alphabetically when we import them, so that git
diffs remain minimal (in particular: the OUI databases we import are not
sorted, and not stable)