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

static/assets/bootstrap/sass/utilities/_position.sass

@@ -0,0 +1,33 @@
+// stylelint-disable declaration-no-important
+
+// Common values
+
+// Sass list not in variables since it's not intended for customization.
+// stylelint-disable-next-line scss/dollar-variable-default
+$positions: static, relative, absolute, fixed, sticky
+
+@each $position in $positions
+  .position-#{$position}
+    position: $position !important
+
+// Shorthand
+
+.fixed-top
+  position: fixed
+  top: 0
+  right: 0
+  left: 0
+  z-index: $zindex-fixed
+
+.fixed-bottom
+  position: fixed
+  right: 0
+  bottom: 0
+  left: 0
+  z-index: $zindex-fixed
+
+.sticky-top
+  @supports (position: sticky)
+    position: sticky
+    top: 0
+    z-index: $zindex-sticky