Automatically convert any MiOS Epoch-style date into what's needed for openHAB, if the corresponding bound Item is of type DateTime.

MiOS uses Epoch-style dates in a variety of the shipped UPnP StateVariable declarations, as well as many of the custom ones defined by Developers.  This code is more general, and replaces the static-list of UPnP Service/StateVariables previously used (Long -> DateTime conversion)