[Bug] Video boolean attributes breaks on import

[giorgiosjames]

Explanation
Using https://grapesjs.com/demo.html v0.15.8 on Chrome 77.0.3~ Windows 10 Pro Build 18362
Importing a Video component with any Boolean attribute (controls, loop, autoplay) using the import modal will break all boolean attributes on the component until the component is deleted.

Reproduction Steps

• Navigate to https://grapesjs.com/demo.html
• Clear the canvas
• Drag in a 'Video' Block
• Ensure the 'Controls' boolean attribute is checked (should be by default)
• Open the import code modal
• Click import
• Boolean attribute traits no longer work on the component
• Also can't re-import the video with the boolean attribute removed

Screencast
Screencast showing video working as expected, and then the bug.

[artf]

At first look the issue might be here:
https://github.com/artf/grapesjs/blob/a850a305b80b8f86c0e7e4fb92b6492c2e5a1957/src/dom_components/model/ComponentVideo.js#L115-L117

indeed in the export/import I'd expect just ... controls> and not ... controls="controls">. The HTML code generator should use single attributes when encounters Boolean true values, so the first try might be

if (this.get('loop')) attr.loop = true;
...