Es add entity set

[ericgsmith]

This includes the set entity method that is on the v3.1 branch.

The previous test fails on Drupal 8.3 as the php unit autoload logic has changed. I have manually loaded the file - but I am not sure if this is the correct approach.

In drupal_phpunit_get_extension_namespaces function the logic has changed so the autoload will only recognise the following directories $suite_names = ['Unit', 'Kernel', 'Functional', 'FunctionalJavascript'];

I can't find examples of how to load in our additional Fixtures directory - however this will for know at least stop the test from failing.

[itarato]

@ericgsmith Hey homie, I realized why I don't like this code. The entity controller suppose to be a non volatile container, and you exposing the entity setter opens the danger of anyone changing the content anytime. Please - unless you have a better idea - add a check in the setEntity method to verify that the entity given has exactly the same type-bundle-id triplet. If not, better to throw an exception or reject it.