Implement event bus

[kraleppa]

The goal of this task is to create the event bus and API for it. It should be based on PubSub. We are going to have 3 separate PubSub processes and each of them will handle following topics:

First PubSub lvdbg channels:
lvdbg/*
lvdbg/{PID}

Second PubSub lvdbg/traces channels:
lvdbg/traces/*
lvdbg/traces/{PID}

Third PubSub lvdbg/states channels:
lvdbg/states/*
lvdbg/states/{PID}

API should cover broadcasting events and subscribing to topics.
There should be such (name can be changed) functions for publishing messages:

1. broadcast_standard(event) => sends event to lvdbg/*
2. broadcast_standard(event, pid) => sends event to lvdbg/*and lvdbg/{PID}
3. broadcast_traces(event) => sends event to lvdbg/traces/*
4. broadcast_traces(event, pid) => sends event to lvdbg/traces/* and lvdbg/traces/{PID}
5. broadcast_state(event) => sends event to `lvdbg/states/*
6. broadcast_state(event, pid) => sends event to lvdbg/states/* and lvdbg/states/{PID}