⚠️ 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/atoms/LinkChange.svelte

@@ -1,10 +1,9 @@
 <script>
     export let href = '#'
     export let text = ''
-    export let noScroll = null
 </script>
 
-<a href={href} class="link-change" sapper-noscroll={noScroll}>
+<a href={href} class="link-change">
     {text}
     <span class="icon">
         <slot></slot>