Mario: reimplementation of Snooze scheduling

+ Follow Snooze protocol closely (discussion with MSimonin)
   Includes, among others:
   - Multicast, GL, GM, GL creation and failures
   - LC, GM join
   - GL election
   - Heartbeats
   - Almost all communication via standard inboxes
   - TODO: few missing features (use Entropy for
           scheduling, failure combinations to be verified,
           ...)

 + First tests passed for all features
   - TODO: some add. synchro necessary (some tests pass
           with sleep periods but not without)
   - TODO: large-scale tests