Moved mobile nav toggle to header

Even though functionaly, the toggle relates to the
left-side panel, it still resides in the breadcrumbs
component. This commit moves the styling to header.scss
that is responsible for styling the breadcrumbs.

app/assets/stylesheets/framework/contextual_sidebar.scss

@@ -429,30 +429,6 @@
   display: none;
 }
 
-.toggle-mobile-nav {
-  display: none;
-  background-color: transparent;
-  border: 0;
-  padding: 6px 16px;
-  margin: 0 0 0 -15px;
-  height: 46px;
-  color: $gl-text-color;
-
-  @include media-breakpoint-down(sm) {
-    display: flex;
-    align-items: center;
-
-    i {
-      font-size: 18px;
-    }
-
-    + .breadcrumbs-links {
-      padding-left: $gl-padding;
-      border-left: 1px solid $gl-text-color-quaternary;
-    }
-  }
-}
-
 @include media-breakpoint-down(sm) {
   .close-nav-button {
     display: flex;

app/assets/stylesheets/framework/header.scss

@@ -605,3 +605,27 @@
 
   @include media-breakpoint-down(xs) { margin-right: 3px; }
 }
+
+.toggle-mobile-nav {
+  display: none;
+  background-color: transparent;
+  border: 0;
+  padding: 6px 16px;
+  margin: 0 0 0 -15px;
+  height: 46px;
+  color: $gl-text-color;
+
+  @include media-breakpoint-down(sm) {
+    display: flex;
+    align-items: center;
+
+    i {
+      font-size: 18px;
+    }
+
+    + .breadcrumbs-links {
+      padding-left: $gl-padding;
+      border-left: 1px solid $gl-text-color-quaternary;
+    }
+  }
+}