Handle SIGTERM exit signals (allows clean exit with systemd)

src/Application.ts

@@ -86,6 +86,7 @@ export default abstract class Application implements Extendable<ApplicationCompo
         process.once('SIGINT', exitHandler);
         process.once('SIGUSR1', exitHandler);
         process.once('SIGUSR2', exitHandler);
+        process.once('SIGTERM', exitHandler);
         process.once('uncaughtException', exitHandler);
 
         // Register migrations