HTML embed feature

This test has changed the CSP definitions:

<meta http-equiv="Content-Security-Policy" content="
    default-src 'none';
    media-src 'self';
    connect-src 'self' https://cksource.com http://*.cke-cs.com;
    script-src 'self' https://cksource.com;
    img-src * data:;
    style-src 'self' 'unsafe-inline';
    frame-src *"
>

After the editor initialization, it should contain 8 widgets with embedded HTML:

• video
• audio
• picture (resize the window to see other images, limits: 1200px, 650px)
• iframe
• table
• text with comment
• comment
• empty

By default, the "previews in view" mode is enabled. It means that previews should be visible.

• If no preview is available (e.g. the only content of HTML snippet is a comment or script), the text "No preview available" should be displayed.
• If the HTML snippet is empty, the text "Empty content" should be displayed.

We use the sanitize-html package to clean up the input HTML. It means that some of the elements or attributes may be not rendered in the editing view. However, they still will be returned in the editor's data.

You can disable the preview mode and have the textarea element that will be blocked or enabled (depends on feature state).

For toggling the state (edit source / see preview), click the icon in the right-top corner.

If the HTML snippet is selected none of the commands for inserting an object should be enabled (media, html-embed, table).