Reorganisation ? of cheating strategies

[drvinceknight]

In #1388 the cheating strategies were removed as well as a bunch of functionality for them in strategy_utils.py.

These are "historic" to the library and nice fun. I believe there are two options for where we put them:

1. In a separate python library (import axelrod-cheaters).
2. In a module that does not import them directly, so that a user has to specifically go get them if they want them (import axelrod.cheaters)