⚠️ Rework completely how transitions works

- Use Svelte/Sapper native if and transitions to show either the page content or the loader, then load each page animationIn
- Code is safe on SSR side, using process.browser on this if
- The <main> element is on position absolute to fade nicely the different pages
- Code cleaning

src/molecules/Photo.svelte

@@ -46,7 +46,7 @@
 
     <div class="photo__image wrap">
         <div class="align">
-            <a href="/viewer/{location.country.slug}/{location.slug}/{photo.slug}" sapper-noscroll>
+            <a href="/viewer/{location.country.slug}/{location.slug}/{photo.slug}">
                 <picture class="photo__picture">
                     <source media="(min-width: 992px)" data-srcset={getThumbnail(private_hash, 1300)}>
                     <source media="(min-width: 768px)" data-srcset={getThumbnail(private_hash, 992)}>