Sync config to disk when values change
When client code calls Plasmoid.confiuration.a = b the value in the KConfigPropertyMap changes, but the underlying KConfigSkeleton does not have any signals emitted until that value is flushed.
We need to connect it to the existing mechanism to sync changes after a timeout.
BUG: 481085 BUG: 482469 BUG: 482090 BUG: 481113 BUG: 482773 BUG: 483083
(cherry picked from commit c37a224b)