Rich text doesn't show the button to select an image from the server 

Steps to reproduce

1. Go to Web resources app and edit the Text and Image component dialog (/mtk/dialogs/components/textImage.yaml). Add to the RichText field the snippet

   configJsFile: /.resources/ckeditor/config-magnolia.js
   

1. Still in Resources app, open for editing the file /ckeditor/config-magnolia.js

   definition = {
     alignment: false,
     images: true,
     lists: true,
     source: false,
     tables: true,
     colors: null,
     fonts: null,
     fontSizes: null
   }
   

1. Move to Pages app, and create a Text and Image component
2. Clic on the Image icon and check no button for selecting an image is show.

Expected results
On the step 4, a button is shown to show the available images on the server

Actual results
No button is shown so no image can be selected

Workaround
N/A

Development notes
Tho it's possible to show the button overriding the CSS styles, it still doesn't work. Clicking on  it doesn't perform any actions.