remove introduce/authenticate handlers
add blather as dependency
remove EventMachine code
add config keys needed to start XMPP component
set up and run XMPP listener
responders either fail with exception or return
handle XMPP events in Responder
make log method available to XMPP stanza handler
don't parse payload as JSON; it's already parsed XML
move helpers into separate module
remove INTRODUCE job
remove INTRODUCE/AUTHENTICATE specs
use xmpp branch of libertree-client
implement XMPP relay

The server accepts XMPP stanzas on a socket, transmits them as the XMPP
server component on successful parse and relays the response to the
sender. This interface is to be used by the job processor.

As the inputs are not checked, socket permissions should be set such
that only trusted processes can relay messages.
catch connection failure and retry
Merge branch 'master' into xmpp

Conflicts:
	Gemfile.lock
	lib/libertree/server.rb
	lib/libertree/server/responder/dispatcher.rb
rewrite MEMBER-DELETE responder

- simplify checks with `assert`
- use `fail` to respond with error codes
tests: replace log with log_handle
tests: add tests for helper functions
tests: rewrite comment specs