Choose order and visibility of Categories

Hey @artf , we need to be able to change the categories order and visibility when the application starts.

I was able to do it changing the model in the Category and this piece of code in BlocksView.js:

if (category && this.categories) {
      if (typeof category.label == 'string') {
        category = {
          id: category.label,
          label: category.label,
          order: category.order,
          open: category.open,
        };
      }

...and setting the order in a flexbox property.

I wanted to know if you think this is a good approach or you have another suggestion.

I'm willing to do a PR.

Thank you!