Add loading animation to public benchmarks page

[Didayolo]

The page is quite long to load, and we have the following display:

These buttons were hidden in the past but it was buggy so we put them back. The best would be to have a loading animation while it is loading, and then everything appears.

• Add loading animation (Public competition list: add loading animation, lazy loading, hide buttons during loading #1285)

[lbeziaud]

@Didayolo it might be interesting to have smaller and/or compressed logos on this page. Loading for e.g. a beautiful 1.41 MB logo to display a 60x60 px thumbnail is what makes the page slow on my side :)

[Didayolo]

@lbeziaud Very good remark indeed!