⚠️ 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/organisms/Footer.svelte

@@ -17,7 +17,7 @@
             <li>
                 <ul>
                     <li>
-                        <LinkTranslate href="/credits" text="Credits" rel="prefetch" noScroll="true" />
+                        <LinkTranslate href="/credits" text="Credits" rel="prefetch" />
                     </li>
                     {#if $site}
                     <li class="instagram">