Include the "q" URL param (as in `/posts/1234?q=<search>`) on thumbnails
for all users. Previously it was only for logged in users. This lets the
next/previous post navbar beneath posts be used by logged out users.
Refactor the post preview html to use the ViewComponent framework. This
lets us encapsulate all the HTML, CSS, and helper methods for a UI
component in a single place.
See https://viewcomponent.org.