Activity log feature

I make possible to extend the comfortable mexican sofa code, rather then modify it. I'll explain some important lines.
See this line and the name of the method. Here I choose to return the original comfortable mexican sofa code and extract to this method to extend in a subclass here: https://github.com/moneyadviceservice/cms/pull/81/files#diff-cc6e703301c6ed33065f186cec0d2939R21