⚠️ 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/Switcher.svelte

@@ -22,7 +22,7 @@
 
 <div class="switcher {type}">
     <div class="switcher__text" class:empty={!location}>
-        <a href="/" sapper-noscroll>
+        <a href="/">
             {#if !location}
             <span class="top">Houses</span>
             <span class="bottom">
@@ -36,7 +36,7 @@
     </div>
 
     <div class="button-control button-control--dashed switcher__icon">
-        <a href="/choose" aria-label="Change the location" sapper-noscroll>
+        <a href="/choose" aria-label="Change the location">
             <IconGlobe
                 color={type.includes('side') ? '#333' : '#fff'}
                 width={type.includes('side') ? 18 : 24}