Content ODP for signals

SAREF4LIFT defines a content ODP for s4lift:Signal, that convey some information such as a fault, a state, or a measurement. Descendants of s4lift:Signal inherit the saref:hasTimestamp, saref:isAbout, and s4lift:conveys properties defining the timestamp when the signal has been generated, the features of interest that the signal is about, and the states or measurements conveyed, respectively.