Don't allow trigger_error() with a controller

[Nicofuma]

I think that you shoud throw an error for each trigger_error found in a controller and a warning for each trigger_error found anywhere else and if an extension call trigger_error in a "Symfony Event" (i.e. KernelEvents::*) it should be denied

[iMattPro]

Not yet at least. The official Pages and Boardrules extensions are using (sort of) controllers for our ACP pages, and we have found that in those cases we must still use trigger_error. Using the a symfony response is not available to our controllers in the ACP.

i think maybe wait until we can truly not use trigger_error anymore in the ACP.

[Nicofuma]

for the xCP yes, but not for the other controllers^^ (and I really want to try to move the xCP modules to DI and routing or3.2 :))