⚠️ 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/Button.svelte

@@ -2,7 +2,6 @@
     export let href = '#'
     export let type = 'a'
     export let text = ''
-    export let noScroll = null
 </script>
 
 {#if type === 'button'}
@@ -14,7 +13,7 @@
 </button>
 
 {:else}
-<a {href} class={$$props.class ? $$props.class : 'button'} sapper-noscroll={noScroll} on:click>
+<a {href} class={$$props.class ? $$props.class : 'button'} on:click>
     <slot></slot>
     <div class="text" data-text={text}>
         <span>{text}</span>