Adjust service restart and shutdown behavior

Explicitly set control-group kill mode, that is: try SIGTERM first, and
use SIGKILL after a timeout. This exactly defines how bees is running as
a child process within the frontend service starter. Not sure if bees cares
about signals but SIGTERM first seems cleaner. On the way, let bees restart
on abnormal termination.

scripts/beesd@.service

@@ -6,7 +6,10 @@ After=local-fs.target
 Type=simple
 ExecStart=/usr/sbin/beesd %i
 Nice=19
+KillMode=control-group
+KillSignal=SIGTERM
 IOSchedulingClass=idle
+Restart=on-abnormal
 CPUAccounting=true
 MemoryAccounting=true
 # CPUQuota=95%