[4.1] Killed "Entities/" folder

This knocks out BC number 2 in #290.

Dear people who use the master branch, this this will break all the things - sorry! But all you have to do is remove any reference to `Entities/`. For example `Facebook/Entities/FacebookApp` is now just `Facebook/FacebookApp`. A quick search/replace should do the trick!

This kinda looks like a big PR - but I just used phpStorm to refactor the location of the `Entities/*` files and it did all the work. It even updated the docs automatically! Man, phpStorm is pretty amazing really!