Instead of changing the background color of the entire page when you
change modes in the post mode menu (which was ugly, and not obvious what
the colors meant), show a notice and make it so that hovering a post
gives it a blue outline. This indicates that clicking the post will do
something different.
* On the post show page, in the parent/child box, change it so that
currently selected post is more visible. Use a light blue outline
around the current post instead of a dark semi-transparent border.
* Fix it so that there's less empty space around thumbnails in the
parent/child box.
Factor out FontAwesome icons into a set of helpers. This is so that it's
easier to keep track of which icons we're using and easier to change
icons globally.
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.
