remove translations listener

It's not really a listener, in that it's mandatory. Integrated into the
CrudAction class instead.
abstract message texts

make thrown exceptions configurable
make it possible to add replacements
rename message key to messages

to be consistent with other config settings
add the domain used in translations to the messages config too
ignore _loadController for code coverage

since this function loads clases, it's not practical to unit test this
account for error messages
test the shell works with overriden translations domain
add a test for getControllers