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

static/assets/bootstrap/sass/mixins/_grid.sass

@@ -0,0 +1,48 @@
+/// Grid system
+//
+// Generate semantic grid columns with these mixins.
+
+=make-container
+  width: 100%
+  padding-right: $grid-gutter-width / 2
+  padding-left: $grid-gutter-width / 2
+  margin-right: auto
+  margin-left: auto
+
+// For each breakpoint, define the maximum width of the container in a media query
+=make-container-max-widths($max-widths: $container-max-widths, $breakpoints: $grid-breakpoints)
+  @each $breakpoint, $container-max-width in $max-widths
+    +media-breakpoint-up($breakpoint, $breakpoints)
+      max-width: $container-max-width
+
+=make-row
+  display: flex
+  flex-wrap: wrap
+  margin-right: $grid-gutter-width / -2
+  margin-left: $grid-gutter-width / -2
+
+=make-col-ready
+  position: relative
+
+  // Prevent columns from becoming too narrow when at smaller grid tiers by
+  // always setting `width: 100%;`. This works because we use `flex` values
+  // later on to override this initial width.
+  width: 100%
+  min-height: 1px
+
+  // Prevent collapsing
+  padding-right: $grid-gutter-width / 2
+  padding-left: $grid-gutter-width / 2
+
+=make-col($size, $columns: $grid-columns)
+  flex: 0 0 percentage($size / $columns)
+
+  // Add a `max-width` to ensure content within each column does not blow out
+  // the width of the column. Applies to IE10+ and Firefox. Chrome and Safari
+  // do not appear to require this.
+  max-width: percentage($size / $columns)
+
+=make-col-offset($size, $columns: $grid-columns)
+  $num: $size / $columns
+
+  margin-left: if($num == 0, 0, percentage($num))