feat(web): use history routing and preserve scroll on filter changes

reaction_board/web/static/index.html

@@ -13,7 +13,7 @@
 <body>
   <div class="app" id="app">
     <header class="topbar">
-      <a class="brand" href="#/home">
+      <a class="brand" href="/home">
         <span class="brand-mark">咻</span>
         <span class="brand-text">
           <strong>Reaction 看板</strong>