build/automake: Include local headers before system-wide headers.

Previously, building would break if a new function was added to the header
files and used, since `make` would still try to use the old system-wide
headers.
Change obworker daemon user to 'ob' (which is created in setup.sh and also used by obbalancer).
Update comments and message text to make it clear to the user and developer that setup.sh *requires* that dependencies are installed and configured in default paths (as defined by install-sx.sh).
fetch_stealth in obelisk.
remove balancer.
remove control message stuff in favour of something simpler.
remove balancer code.
add heartbeat.
cleanup code slightly.
zmq server side encryption.
re-enable auth and cert stuff.
config allowed certs directory where client pubkeys are installed.
port to czmq++ with crypto.
ability to enable/disable crypto (disabled by default).
enable whitelist even when crypto is disabled.
remove checksum field - it's not needed.
remove checksum from documentation as it's not needed.
update docs further.
made scary sounding warning sound less severe.
Merge branch 'origin/master'