[Sponsors] Rotation Silver and Bronze sponsors

[jlbellido]

Follow-up to #32

The current status is we have the complete list of sponsors, but we need to display the silver and bronze sponsors smaller than they are currently and with a rotation block using a carousel.

Tasks:

Backend

• [x] Integrate the slick.js library with the project.
• [x] Display the Bronze and Silver sponsors using the rotation theme with the AllSponsorsBlock.

Frontend

• [x] Customize the carousel according to the breakpoints of the project.
• [x] Apply the styles for showing them inside the sponsors wrapper.

[jlbellido]

Hi! This tickets depends on https://github.com/AsociacionDrupalES/devdaysseville/pull/99. Since this is big change in the sponsors section, I wouldn't like to merge this until having the frontend part done.

How to work on this?

• Create a new branch from your dev branch like an other normal ticket.
• Fetch the changes introduced in the other branch: git pull https://github.com/jlbellido/devdaysseville.git sponsors_jcarrusel
• Commit your changes from the front end part.
• Push your changes as usual and send a pull request.
• You will noitices that all commiits will be there (yours and that ones done prviously)

Possible issues and how to solve

• I'm not having content: Create several sponsors. You can use devel generate.
• The js is not working: Clear the cache, the new library needs to be loaded.

[jlbellido]

The backend part done.

[jlbellido]

Looks really nice @babette-landmesser thanks for your time and awesome work here!