New MqttLimit interface limits the amount of ongoing connections

tng-push patches

This reverts commit d844aef, reversing
changes made to f96e48e.

* upstream/master: (62 commits)
  Bumped v2.3.0
  comments clean up
  empty interfaces should not be invalid
  added ws to dev dependencies
  adding unit test for websocket attach
  mqtt over websocket on different path
  enable docker hub builds for Raspberry Pi
  Fixed dockerfile-rpi docker build
  Explicit support of `redisClient({ url })`
  bumped v2.2.0
  forward ascoltatori error events
  added mongo and redis test db to .dockerignore
  removed hiredis
  refactor the test to avoid using timeout
  add test for 'unsubscribe while multi subscriptions' and fix bug
  Fixbug (subscribes with same topic, may lead to the ascoltatore added multi cbs, and can't unsubscribe)
  Bumped v2.1.0
  Rename Server_Wtih_All Interfaces-Settings.js to Server_With_All_Interfaces-Settings.js
  avoid erroring when client disconnect abruptly in tests
  fix broken tests on travis?
  ...