Add the ability to execute commands on the rich text area from JavaScript

Extend the JavaScript API of the editor with a method to access the command manager used by the rich text area. This way we will be able to execute commands on the rich text area from JavaScript code like this:

if ( editor.getCommandManager().isEnabled('forecolor') ) {
    editor.getCommandManager().execute('forecolor', 'yellow');
    alert( editor.getCommandManager().getValue('forecolor') );
}