Simplify import logic across all layouts

[naher94]

I have to include several files across several layouts which is causing misses. Would be good to have a way to reduce number of places I need to include all the files such as {% include easter-egg-snackbar.html %}, {% include tag-manager.html %} and {% include header.html %}

Also note that the easter-egg-banner does not current fly over the top of hero images because of where it sits in the DOM

default.html, default-hero.html and blank.html are the 3 base layouts as if today that need consolidated. post-hero.html also contains some include logic