Refactor event queue, message queue and cbus

[alyapunov]

1. There is an opinion that cbus is not obvious and not optimal.
2. I've read sources of ev library and would be glad if we use something more readable, maybe uv library.
3. I have suspicions that message queue between iproto and TX does not handle correctly with TX overload case. At least I cannot understand how it can work optimally with rlists in this case (cosider dpdkey queue).

I'm not sure all the thing above must be refactored and fixed but at least they should be investigated.