Split the Logo into a separate HTML element

The main objective with this MR is to create a separate element for the Logo, so that it can have its own link target.

That change happens in the header-content template, but some CSS changes were also necessary.

• I added a class for the Document Title (main-title) and changed the CSS referring to it to use that classname rather than :first-child. It part, this is clearer as to what it does, and in part it was required because the main title is now the second child.
• As a separate element, rather than a ::before, we have a bit more flexibility on arrangement. I took the opportunity to tighten up the logo spacing, and to make it scale relative to the navbar height. I envision future UI changes that make this navbar larger, and it makes sense to scale the logo with it.
• The pipeline wasn't building a bundle-dev, so I altered the logic to make it work. Intended as a fast patch, we probably want to revisit the logic here eventually.