[UX] Mobile project browser: decrease amt of scrolling needed on Mobile

This issue was spun off from https://github.com/backdrop/backdrop-issues/issues/3092

The worst thing here is too much scrolling, combined with the fact that the installation queue is at the bottom of the page.

Original suggestion from @klonos:

Trim the project descriptions more than the non-mobile version, or even consider using some sort of accordion solution here (is it possible to collapse all rows that are outside the viewport, and only expand those that come into view via javascript?). Another alternative is to convert this vertical list to a horizontal one that can be flipped left/right. This will bring the installation queue closer.