Flexbox sticky footer (#2289)

* Remove sticky footer JavaScript

* Use flexbox to force footer to the bottom of every page

* Fix flexbox in Internet Explorer

_sass/minimal-mistakes/_page.scss

@@ -19,6 +19,22 @@
   }
 }
 
+body {
+  display: -webkit-box;
+  display: -ms-flexbox;
+  display: flex;
+  min-height: 100vh;
+  -webkit-box-orient: vertical;
+  -webkit-box-direction: normal;
+  -ms-flex-direction: column;
+          flex-direction: column;
+}
+
+.initial-content,
+.search-content {
+  flex: 1 0 auto;
+}
+
 .page {
   @include breakpoint($large) {
     float: right;