Redesigning the default category page

[zogstrip (Régis Hanol)]

@sam

The current plan is for @zogstrip to urgently add a site setting for “category page style”:

• Default - the new default with the 50/50 view
• Classic - for old default
• Categories Only: for categories only without listing topics.

The desktop_category_page_style is now in

https://github.com/discourse/discourse/commit/4d6028ea2db6f1abf1041a10b26692b3b41a7b42

I changed the name of the style a bit

• Default → “Categories and Latest Topics”
• Classic → “Categories with Featured Topics”
• “Categories Only” stayed the same.