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

static/assets/bootstrap/sass/mixins/_hover.sass

@@ -0,0 +1,31 @@
+// Hover mixin and `$enable-hover-media-query` are deprecated.
+//
+// Originally added during our alphas and maintained during betas, this mixin was
+// designed to prevent `:hover` stickiness on iOS-an issue where hover styles
+// would persist after initial touch.
+//
+// For backward compatibility, we've kept these mixins and updated them to
+// always return their regular pseudo-classes instead of a shimmed media query.
+//
+// Issue: https://github.com/twbs/bootstrap/issues/25195
+
+=hover
+  &:hover
+    @content
+
+=hover-focus
+  &:hover,
+  &:focus
+    @content
+
+=plain-hover-focus
+  &,
+  &:hover,
+  &:focus
+    @content
+
+=hover-focus-active
+  &:hover,
+  &:focus,
+  &:active
+    @content