Added wave spread animation

[teobais]

Hello,

this is my very first trial on Sass and one of the first for front-end stuff, so, any feedback would be helpful.

From what I see, the implemented animation is not as rapidly evolved as the rest of the existing ones, but I thought of having an overall feedback, as a first step.

TB

[tobiasahlin]

Feel free to rework this into the new structure as of #143 🙏