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.
Common
* Replace LocalDateTime with Instant everywhere
Client
* Display message creation date with system time zone in MessageControl
* LocalDB#users now strictly contains Users
* lastSync time stamp in LocalDB (saved per user)
* isOnline parameter in save function (lastSync updated if true)
* lastSync time stamp in LoginCredentials
* No ClientConfig#getLoginCredentials because of missing information,
moved to LoginScene
* Pass LocalDB#lastSync to LoginCredentials in LoginScene
Server
* Explicit lastSync parameter for
PersistenceManager#getPending(Group)Messages
This sends the correct time stamp to the server, however the JPQL
queries have yet to be adjusted.