No validation messages shown on channel settings page

If you save channel settings but leave a required field empty field and caption turn red, but not message is shown ("XXX is a required field"). To align this with other editors we should show those messages.

It will also remove warnings in the browser console like:

mdInput messages show animation called on invalid messages element:  jQuery.fn.init [md-input-container.md-block.qa-field-requiredString.flex.ng-animate.md-input-invalid]