Don't set datetime when auto time sync is enabled
This became more visible because we were calling timedate1_call
at startup, on widget creation the signals were getting emitted.
By moving the g_signal_connect_* calls into the class' init we avoid the startup activation.
Let's also not call timedate_1_call to set the time when Network time synchronization is active, because this call will fail with:
GDBus.Error:org.freedesktop.timedate1.AutomaticTimeSyncEnabled: Automatic time synchronization is enabled
Fixes #2945 (closed)