Only EE supports multiple issue assignees, so this CE code should not contain
code to have multiple assignees. EE will override the multiple issue assignees
feature by overriding this method.
By changing this text the css will check for `toggle_text == default_label`. In this case they were not the same.
Now they are and it will show the default label in gray.
- Some views had a "Close" button. We've removed this, because we don't
want users accidentally hiding the validation errors and not knowing
what needs to be fixed.
- Some views used `li`, some used `p`, some used `span`. We've
standardized on `li`.
- Some views only showed the first error. We've standardized on showing
all of them.
- Some views added an `#error_explanation` div, which we've made
standard.
