Reworked networking to share threads between interfaces.

This reduces number of used threads for I/O to constant:
 CPU_COUNT * 3 instead of IF_COUNT * (CPU_COUNT * 3 + 1)
Merge branch 'development' into netperf
Merge branch 'development' into netperf
Merge branch 'development' into new_iohandler
Merge branch 'development' into new_iohandler
Merge branch 'development' into new_iohandler
key parsing: default origin, TTL and class; parse as a last line

refs #2353
Updated version to 1.2.0 final.
Added missing hattrie free.
Fixed coverity errors in rrset_tests - wrong reads, memory leaks.

- Coverity: 989773, 989769, 989768, 989602, 989600
Free trie on failed transfer.
man: move to subdirectory, insert version using autotools
add missing quote into sample configuration file
add missing quote into sample configuration file
Reimplemented XFR handler to support queueing.

Requests are now scheduled in FCFS manner, while there
can be a fixed amount of pending requests from N threads.
Currently the limit is set to 10 parallel requests to honor
BIND9 default setting, but should be configurable.

To do:
- Fetch pending request state for 'zonestatus' command
- As of now, there can be a multiple NOTIFY tasks,
  would it be a problem?
- Cleanup of the xfr_answer()
- Check for bugs
Fixed default RRL slip.
Configurable number of parallel xfers (system.transfers).

Updated documentation, cleanup.
Merge branch 'new_iohandler' into development

Conflicts:
	src/knot/server/xfr-handler.c
Merge branch 'master' into development

Conflicts:
	man/knot.conf.5in
	man/knotc.8in
	man/knotd.8in
	src/knot/conf/conf.c
Fixed default config values for unittests.