This reverts merge request !532

closes #344

Most of the files were moved to knot/common/ (ex knot/other/).

Two files moved to utils, because were used only there
(hex, strtonum).

One file (strlcat) moved to libknot/internal/, as it was used both
in server and in libknot. (Also, strlcpy was there already).

Symbols in libknot/internal/ should not have knot_ prefix unless
they are a replacement for a system function.

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

Closes #262

- Checks if events can be replanned before doing so.
- Duplicates DDNS queue after reloads.

Two configurable options:
- wait for zones to be loaded before starting (default)
- start server and load zones in the background (asynchronous-start on)