App drawer: app grid layout

If we're going to support larger screens better we need a way for the app drawer to work well across these.

In my view, this is the best path forward at the moment:

• We keep a fixed number of apps per page, regardless of form factor (otherwise we lose the benefits of pagination for finding apps)
• The apps on a page flow from the top left to the bottom right, and there can be empty spots at the end
• Apps can be freely re-arranged and moved between pages via drag & drop
• 24 seems like a good number of apps per page, because it's in the ballpark of what other systems have (usually 20-30 per page, regardless of screen size) and it's divisible by 3, 4, 6, and 8 (which allows for flexible re-layouting)
• No fixed favorites row, as that would not work if the number of icons per row change. Instead, you can freely move icons around on the pages, and the first row of apps on the first page is a sort of "implicit" set of favorites

So on phones we'd have 4x6 apps per page:

On larger, landscape screens we'd have the same number of apps, but laid out differently, e.g. 6x4 or 8x3: