fixes #211

Conflicts:
	src/knot/server/zones.c

cov#1168292

* events now carry pointer to their scheduler
* no event types, events are simple callbacks
* removed unused or deprecated stuff
* bugfix: zone never expired since expire was initialized on create
* bugfix: race condition on rescheduling events
  - there is always some time between cancel and schedule
  - if two threads run run past the cancel and then race for schedule,
    they may rarely schedule an event two times
  - this is hard to deal with unless we place a lock on the zone
    operations, therefore each schedule checks heap if the event is not
    already scheduled and if it is, it replaces the old instance

* zone timers are frozen before zonedb reconfigure
* zone timers are rescheduled after zonedb is reconfigured & published

refs #209
fixes #202

* removed redundant attributes
* removed unused parameter occurences
* moved related functions to appropriate files
* evsched has now context (server)
* zone does not point to server
* zone event planning is still in the zone loading and requires server #209

Old API required to create duplicate fake zone with switched contents.

This patch disconnects contents from the old zone, so it may introduce
a short period where it answers SERVFAIL. Ownership of the zone/contents
must be resolved as part of the #209.

also includes removal of knot_ prefixes from private API

close #205

- NOTIFY/SOAs now can be signed.
- Transaction security is checked.
- TSIG is checked before evaluating zone state.

Current approach creates duplicate symbols when linking the library,
the simpliest solution is to make zscanner dependent on libknot.

issue #1

issue #1

issue #1

issue #1

issue #1

The signatures are now refreshed (signature_lifetime / 10) seconds
before their expiration. The default signature lifetime is 30 days,
therefore the signatures are refreshed 3 days before their expiration.

The parameter 'expires_at' in signing functions was renamed to 'refresh_at',
as the name was misleading.

The signing policy structure was cleaned and helper functions were added.

DNSSEC event logging was changed from relative to absolute value, because
the intervals are much longer now.

- Dropped unused adjusting functions
- Moved one into xfr-in.c
- Removed obsolete API parameters for changeset application funtion

This prevents creating journal if it didn't exist before and we
only want to read from it. Journal sync and reload caused this.

new_serial should be initialized

- just a hotfix, a proper solution is to get rid of zone_contents->zone link, it's not really needed.

The purpose is to observe the behavior of 1.4.1 compared to 1.4.0
refs #187