moved everything to webpack, migrated to bootstrap v4

src/frontend/views/footer.html

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+<footer>
+  <p>
+    &#169;2018 - 2019 Felix Hartmann | SlowDowner v3 | <label id='user_count'>Verbundene Geräte: 0</label> | 
+    built and hosted on <i class="fab fa-linux"></i> | <a target='about:blank' href="https://gitlab.ffhartmann.de/felixh/slowdowner">Source</a> |
+    <a target='about:blank' href="https://gitlab.ffhartmann.de/felixh/slowdowner/raw/master/LICENSE">License</a> | Genutze OpenSource Projekte:
+    <a target='about:blank' href="https://pdfobject.com">PDFObject</a> & <a target='about:blank' href="https://howlerjs.com/">howler.js</a> |
+  </p>
+</footer>

src/frontend/views/head.html

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+<meta charset="UTF-8"> 
+<meta name='viewport' content='width=device-width, initial-scale=1.0'>
+<link rel='shortcut icon' type='image/png' href='../images/snail.png'/>
+<script src='/socket.io/socket.io.js'></script>

src/frontend/views/menu.html

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+<nav class='navbar navbar-dark navbar-expand-sm bg-dark'>
+  <div class='container-fluid'>
+    <a class="navbar-brand" href="/">
+      <img src="../images/snail.png" width="30" height="30" alt="SlowDowner Logo">
+    </a>
+    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
+      <span class="navbar-toggler-icon"></span>
+    </button>
+    <div class="collapse navbar-collapse" id="navbarNav">
+      <ul class="navbar-nav">
+        <li class="nav-item">
+          <a class='nav-link' href='/'><i class="fa fa-music"></i> Musik</a>
+        </li>
+        <li class="nav-item">
+          <a class='nav-link' href='/sheets.html'><i class="fa fa-file"></i> Noten</a> 
+        </li>
+      </ul>
+    </div>
+  </div>
+</nav>