Use twig for logging
permit empty keys arrays when posting to a view (FB 12416)
Add distribution stats to _system

BugzID: 12555

Conflicts:
	src/chttpd_misc.erl
Expose message queue lengths.

Conflicts:
	src/chttpd_misc.erl
Track message queue lengths of all registered pids

Simple update that reports the message queue lengths of every registered
process.

BugzId: 13797

Conflicts:
	src/chttpd_misc.erl
s/couch_config/config
Use os:timestamp/0 instead of now/0
Do not log client disconnects as errors

In the future it would be nice to collect metrics of these, but
practically speaking we already have them in the HAProxy logs.

BugzID: 14090

Conflicts:
	src/chttpd.erl
Pull up couch_httpd:body/1
Reorder clauses to reduce diff noise
Check that a request body was sent before decoding

BugzID: 14114