Add responsiveness for footer. Update gulpjs, package.json and bootstrap sass

static/assets/bootstrap/sass/utilities/_display.sass

@@ -0,0 +1,68 @@
+// stylelint-disable declaration-no-important
+
+//
+// Utilities for common `display` values
+//
+
+@each $breakpoint in map-keys($grid-breakpoints)
+  +media-breakpoint-up($breakpoint)
+    $infix: breakpoint-infix($breakpoint, $grid-breakpoints)
+
+    .d#{$infix}-none
+      display: none !important
+
+    .d#{$infix}-inline
+      display: inline !important
+
+    .d#{$infix}-inline-block
+      display: inline-block !important
+
+    .d#{$infix}-block
+      display: block !important
+
+    .d#{$infix}-table
+      display: table !important
+
+    .d#{$infix}-table-row
+      display: table-row !important
+
+    .d#{$infix}-table-cell
+      display: table-cell !important
+
+    .d#{$infix}-flex
+      display: flex !important
+
+    .d#{$infix}-inline-flex
+      display: inline-flex !important
+
+//
+// Utilities for toggling `display` in print
+//
+
+@media print
+  .d-print-none
+    display: none !important
+
+  .d-print-inline
+    display: inline !important
+
+  .d-print-inline-block
+    display: inline-block !important
+
+  .d-print-block
+    display: block !important
+
+  .d-print-table
+    display: table !important
+
+  .d-print-table-row
+    display: table-row !important
+
+  .d-print-table-cell
+    display: table-cell !important
+
+  .d-print-flex
+    display: flex !important
+
+  .d-print-inline-flex
+    display: inline-flex !important