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

static/assets/bootstrap/sass/utilities/_sizing.sass

@@ -0,0 +1,14 @@
+// stylelint-disable declaration-no-important
+
+// Width and height
+
+@each $prop, $abbrev in (width: w, height: h)
+  @each $size, $length in $sizes
+    .#{$abbrev}-#{$size}
+      #{$prop}: $length !important
+
+.mw-100
+  max-width: 100% !important
+
+.mh-100
+  max-height: 100% !important