Add a setStatus() method for configuration entities

As a follow up to #1826602: Allow all configuration entities to be enabled/disabled, Let's add a setStatus() method on configuration entities. enable/disable methods would then just wrap this.

Here is an initial patch. It just adds this as a method to ConfigEntityBase, no interfaces etc..

I guess the question is do we want this to be a part of the ConfigEntityInterface? This could mean all of them, or remove enable/disable and just have setStatus in the interface.