Ignoring events propagation

It's a test for ignoring events fired in elements with a data-cke-ignore-events attribute (#4600).

Events are logged in the browser's console.

Case 1: Events ignoring

1. Focus the widget by clicking it.

2. Move mouse cursor over the left container (Ignored container with data-cke-ignore-events="true").

3. Keep moving the cursor over the container.

   Expected: no further "Received mousemove event." logs are added.

4. Click on a "Click!" button in the container.

   Expected: No "Received click event." gets logged.

5. Click on the text input in the container.

   Expected: Text input gets focused.

6. Type few characters into the focused input.

   Expected: Text is inserted. No keyboard events are logged.

Note: you might get unexpected focus nad blur events in the process, it's a known issue.

Case 2: Container without event ignoring

1. Focus the widget by clicking it.

2. Move mouse cursor over the right container (Regular container).

3. Keep moving the cursor over the container.

   Expected: "Received mousemove event." logs are added.

4. Click on a "Click!" button in the container.

   Expected: "Received click event." is logged.

5. Click on the text input in the container.

   Expected: Click events are logged. Editor decides what to do with the selection.

Case 3: imageLoaded event

1. Reload the page (test).

2. Check the console.

   Expected: There's only one Received imageLoaded event. log.