[BSv5] Replace media styles with flex equivalents

[chalin]

Replace the BSv4 media component used in the blog list page, layouts/blog/list.html. For details, see Media object from the BSv5.2 docs.

Here are the former style definitions:

.media {
    display: flex;
    align-items: flex-start;
}

.media-body {
    flex: 1;
     // -> flex-grow: 1;
     // -> flex-shrink: 1;
     // -> flex-basis: 0%;
}

Strange, I recall working on style definitions for .media and .media-body, but I can't find them -- so currently they are undefined.

As a result, the Docsy-example blog page can look like this:

It's because of the figure, which is made more obvious in this screenshot: