Unify epislon-greedy

[laszukdawid]

What

Each agent has built-in epsilon greedy mechanism. There's likely little need to have the same code everywhere so it should be moved to a single place.

Consideration

As it is right now, and as it is intended, each agent needs to touch (agent.act) state to provides an action. This touch can be related to increment some internal counter or producing additional values, e.g. entropy. Only touched state (all data tuple) is used in step to learn something.