Channel handling: have a dedicated event topic per event key

[Lance-Drane]

Currently, the events channel looks like this:

<organization>/<facility>/<system>/<subsystem>/<service>/events

This publishes all events to a single channel, which has some problems regarding authorization (plus requiring clients to perform excessive control flow branching).

A better approach may be:

<organization>/<facility>/<system>/<subsystem>/<service>/events/<event_name>

where event_name represents an event key.