Visual editor does not work with the label horizontal: true

[BBE-FR]

Visual editor is a very nice addition to the latest version !!

It is working well, even if you use an horizontal stack inside a custom vertical stack to create a "fake" custom horizontal stack with visual editor:

like this

type: custom:vertical-stack-in-card
cards:
  - type: horizontal-stack
    cards:
      - type: custom:mushroom-template-card
      etc...

You can see that in this case we have the same issue as #150

But if you try to use the label horizontal: true to get rid of the horizontal stack, it works very well in YAML, without the borders appearing, but the visual editor is broken:

type: custom:vertical-stack-in-card
horizontal: true
cards:
  - type: custom:mushroom-template-card
  etc...

The visual editor does not work anymore:

With the following warning (translated from french) :

Visual editor is not available for this configuration:
- "horizontal" key not expected or not available for visual editor 
You can edit your configuration through YAML

I know the card is named vertical-stack-in-card but it works so well that I think the horizontal option deserve to be implemented in the editor...