⚠️ 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/Location.svelte

@@ -7,7 +7,7 @@
 </script>
 
 <div class="location">
-    <a href="/location/{country.slug}/{slug}" rel="prefetch" sapper-noscroll>
+    <a href="/location/{country.slug}/{slug}" rel="prefetch">
         <img src={country.flag.full_url} alt="Flag of {country.name}">
         <div class="anim-mask mask-city">
             <h3 class="location__city">{name}</h3>