This class is different from the others in this module. Its purpose
is to transfer values from deprecated GSettings keys to the preferred
keys on startup, and keep them synchronized at all times for backward
compatibility.
Initial deprecated keys being handled are:
"week-start-day" (org.gnome.evolution.calendar)
"working-days" (org.gnome.evolution.calendar)
Listens for "client-created" signals from its EClientCache. If the
newly-created client is an ECalClient, automatically configure its
default timezone from EShellSettings.
Collect all the "config" extensions from the "addressbook", "calendar",
and "mail" modules into one place. These extensions typically just bind
GObject properties of extensible classes to app-specific GSettings keys.
