Add an aspect ratio prop to Carousel component

[Phixyn]

The Carousel should have an aspect ratio prop that can be passed to it. Then, on the CMS, we could include the aspect ratio of images expected to be in the carousel. In the carousel component, we would use the aspect ratio to add a Bulma class to the figure element:

<figure class="image is-5by3">

There might be a problem if we want to use images with different aspect ratios in a single carousel. In that case, we might have to crop images or resize them accordingly.

See also: https://bulma.io/documentation/elements/image/#responsive-images-with-ratios