Resolve "Rocket Chat iframe integration doesn't work well on production"

We introduce a new Global Event "ready" in Rocket Chat in release 5.4.3-hive.4. Then we use it in RocketChatWidget.jsx. We wait for a message informing about this event as a signal, that Rocket Chat application is ready to handle post messages being sent to it. We haven't waited for Rocket Chat's readiness before and this was causing unexpected, random behavior in handling of iframe.

We also created a Logger service, for secure logging on production.

Closes #210 (closed)