Make it possible to register event listeners on instance creation

[Frederico Caldeira Knabben]

The following currently doesn't work in all cases:

var editor = editor.replace( 'editor1' );
editor.on( 'someEvent', function() { ... } );

... because the event may be fired during the "replace" call, so the event registration comes too late.

There are ways to do so, but it's a little cumbersome:

CKEDITOR.on( 'instanceCreated', function( ev )
    {
        ev.editor.on( 'someEvent', function() { ... } );
    });

editor.replace( 'editor1' );

There should be instead a way to do that on instance creation, just like this:

editor.replace( 'editor1',
    {
        // ... some editor settings

        on :
        {
            someEvent : function() { ... },
            otherEvent : function() { ... }
        }
    });

[Frederico Caldeira Knabben]

Fixed with [3267].