Allow Liquid code if input type is liquid

[andershagbard]

This PR allows to use Liquid code, if the input type is "liquid". Prior to this, it would warn the that this was invalid.

E.g.:

{
  "settings": [
    {
      "id": "text_value",
      "type": "liquid",
      "label": "Text Value",
      "default": "{% render 'block' %}"
    }
  ]
}

[aswamy]

This is great stuff @andershagbard ! I just checked out the branch to test it out and it looks great.

[aswamy]

A great follow-up could be for blocks and presets as well. But looks good for now. One minor suggestion before i merge this.

[andershagbard]

Thanks @aswamy. I've committed your suggestion