Add central_frequency and duration values to VOEvents oLIB and MLy
The content of VO alert voevents are missing p_central_freq p_duration for MLy, and p_duration for oLIB. For oLIB was still present the "fluency" that the collaboration has decided not to distribute.
Solve issue: emfollow/gwcelery#594 (closed) #282 (closed)
Edited by Roberto DePietri