Work/change loaded elements

Allow the user to bulk-change elements by providing a json. The changed elements will be just in the current scene so other scenes are unaffected saving a bookmark also saves the new elements.

json in the format:

{
    "elements":[
      {
          "name" : <string>,
          "color" : <hex-string>
      }
   ]
}

Currently only color is supported but it's easy to add more information in the future.