Add a LocalDB auto save mechanism

During startup, a timer is initialized inside the LocalDB which saves it
after 500 milliseconds during startup and then in intervals of 2
minutes, which can be configured in the ClientConfig.

client/src/main/resources/client.properties

@@ -1,8 +1,6 @@
 server=localhost
 port=8080
 localDB=localDB
-password=
-user=
-ignoreLocalDB=false
+localDBSaveInterval=2
 consoleLevelBarrier=FINER
 fileLevelBarrier=OFF