zone-events: Split zone events into 3 files

 - events.c: event manipulation API
 - events-impl.c: zone event implementations
 - events-replan.c: event replanning implementations

Closes #262
unittests: fixed include
zone-events: Whitespace removed
zone-events: renamed files
Merge branch 'events-cleanup' into 'master'

Events cleanup

See merge request !286