Release v4.2.21

Use new versions:

- Products.PloneMeeting = 4.2.8
- Products.MeetingCommunes = 4.2.5
- collective.eeafaceted.z3ctable = 2.25
- imio.actionspanel = 1.64
- imio.pm.locales = 4.2.8
- imio.zamqp.pm = 0.18