[fdsnws-event2mc3] [seiscomp2mc3] : improvements needed

[jmsaurel]

• First arrival station should be checked against station configured in SEFRAN3_Channels.conf.
  Currently, it's not checked and stations not present in the configuration may be added, resulting in incomplete pre-filled form when the automatic entry is reviewed.

• S-P time should be added based on really picked S-phase in the QuakeML/SeisComPML file.
  If no S-phase is found, S-P time should not be added.
  Currently, S-P time is always estimated based on P arrival, station to origin distance and fixed wave speed, when a distance is available.