Load bootstrap as part of the SASS pipeline, instead of via a <link> tag

--> This solves a problem where our _variables.scss could not be used to customize the bootstrap theme

_includes/base/scripts.html

@@ -1,3 +0,0 @@
-<!-- Bootstrap core JavaScript -->
-<script src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.3.1.min.js"></script>
-<script src="http://ajax.aspnetcdn.com/ajax/bootstrap/3.3.7/bootstrap.min.js"></script>

_includes/base/styles.html

@@ -1,10 +1,7 @@
-<!-- Bootstrap core CSS -->
-<link href="http://ajax.aspnetcdn.com/ajax/bootstrap/4.0.0/css/bootstrap.css" rel="stylesheet">
+<!-- Custom styles for this template -->
+<link href={{ "styles.css" | absolute_url }}  rel="stylesheet">
 
 <!-- Custom fonts for this template -->
 <link href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css" rel="stylesheet" type="text/css">
 <link href="https://cdnjs.cloudflare.com/ajax/libs/simple-line-icons/2.4.1/css/simple-line-icons.css" rel="stylesheet">
 <link href="https://fonts.googleapis.com/css?family=Lato:300,400,700,300italic,400italic,700italic" rel="stylesheet" type="text/css">
-
-<!-- Custom styles for this template -->
-<link href={{ "styles.css" | absolute_url }}  rel="stylesheet">

_layouts/default.html

@@ -15,6 +15,5 @@
     {{ content }}
 
     {% include base/footer.html %}
-    {% include base/scripts.html %}
   </body>
 </html>

styles.scss

@@ -2,6 +2,9 @@
 ---
 // Core variables and mixins
 @import "variables.scss";
+
+@import "bootstrap/bootstrap";
+
 @import "mixins.scss";
 // Global CSS
 @import "global.scss";