Issue#553

fix the issue #553 (closed) : the issue was the LocalPVProvider used in Ephemeris to compute the attitude provide only the attitude at the current date, and return an exception if the computed date is not the current date of the propagator. The issue was solved by adding a way for the LocalPVProvider to be used for a different date. Now, there is an Ephemeris object inside the LocalPVProvider with the same parameters as the main Ephemeris, but with no attitude law to avoid infinite loop.