New DNSSEC implementation for Knot DNS 2.0

adds new optional params:

--disable-daemon
--disable-utilities
--disable-documentation

Fixes #328

Namedb leak

Fixes the possible leak of not closing the DB environment.

Note: There's a race condition on the 'if' - threads may avoid closing the env anyway.
To fix that we'd need to introduce locks to namedb.

See merge request !339

CID #1268505

This is a better solution than the previous one as it prefers
not freeing memory to crashing the server.

Better address sanity checks

See merge request !338

Embedded lmdb

This MR changes few things:

- lmbd:MDB_0.9.14 is embedded in src/libknot/internal/namedb/
- embedded LMDB is used when --with-lmdb=no is passed to ./configure
- otherwise shared LMDB is searched for and used (default)

This should make all parties happy.

See merge request !337

TCP hardlimits

Several bugs fixed:

- TCP client count can be limited by the config variable max_tcp_clients in system (so there are free descriptors for autonomous operation)
- Aggressive limits when client connects, but doesn't start sending data in time
- Throttling doesn't affect activity other then accept()
- Possible resource leak on tcp_sweep
- Bad logic (started reading from socket before checking for error activity first)
- Bad logic (could close master socket on fd exhaustion)

fixes #326

The limit is global, threads are allowed equal portions of the limit.

Yparser

See merge request !323

Conflicts:
	src/libknot/errcode.c
	src/libknot/errcode.h