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

static/assets/bootstrap/sass/_button-group.sass

@@ -0,0 +1,151 @@
+// stylelint-disable selector-no-qualifying-type
+
+// Make the div behave like a button
+.btn-group,
+.btn-group-vertical
+  position: relative
+  display: inline-flex
+  vertical-align: middle
+
+  // match .btn alignment given font-size hack above
+
+  > .btn
+    position: relative
+    flex: 0 1 auto
+
+    // Bring the hover, focused, and "active" buttons to the front to overlay
+    // the borders properly
+    +hover
+      z-index: 1
+
+
+    &:focus,
+    &:active,
+    &.active
+      z-index: 1
+
+  // Prevent double borders when buttons are next to each other
+  .btn + .btn,
+  .btn + .btn-group,
+  .btn-group + .btn,
+  .btn-group + .btn-group
+    margin-left: -$btn-border-width
+
+// Optional: Group multiple button groups together for a toolbar
+.btn-toolbar
+  display: flex
+  flex-wrap: wrap
+  justify-content: flex-start
+
+  .input-group
+    width: auto
+
+.btn-group
+  > .btn:first-child
+    margin-left: 0
+
+  // Reset rounded corners
+  > .btn:not(:last-child):not(.dropdown-toggle),
+  > .btn-group:not(:last-child) > .btn
+    +border-right-radius(0)
+
+  > .btn:not(:first-child),
+  > .btn-group:not(:first-child) > .btn
+    +border-left-radius(0)
+
+// Sizing
+//
+// Remix the default button sizing classes into new ones for easier manipulation.
+
+.btn-group-sm > .btn
+  @extend .btn-sm
+
+.btn-group-lg > .btn
+  @extend .btn-lg
+
+//
+// Split button dropdowns
+//
+
+.dropdown-toggle-split
+  padding-right: $btn-padding-x * 0.75
+  padding-left: $btn-padding-x * 0.75
+
+  &::after,
+  .dropup &::after,
+  .dropright &::after
+    margin-left: 0
+
+  .dropleft &::before
+    margin-right: 0
+
+.btn-sm + .dropdown-toggle-split
+  padding-right: $btn-padding-x-sm * 0.75
+  padding-left: $btn-padding-x-sm * 0.75
+
+.btn-lg + .dropdown-toggle-split
+  padding-right: $btn-padding-x-lg * 0.75
+  padding-left: $btn-padding-x-lg * 0.75
+
+// The clickable button for toggling the menu
+// Set the same inset shadow as the :active state
+.btn-group.show .dropdown-toggle
+  +box-shadow($btn-active-box-shadow)
+
+  // Show no shadow for `.btn-link` since it has no other button styles.
+  &.btn-link
+    +box-shadow(none)
+
+//
+// Vertical button groups
+//
+
+.btn-group-vertical
+  flex-direction: column
+  align-items: flex-start
+  justify-content: center
+
+  .btn,
+  .btn-group
+    width: 100%
+
+  > .btn + .btn,
+  > .btn + .btn-group,
+  > .btn-group + .btn,
+  > .btn-group + .btn-group
+    margin-top: -$btn-border-width
+    margin-left: 0
+
+  // Reset rounded corners
+  > .btn:not(:last-child):not(.dropdown-toggle),
+  > .btn-group:not(:last-child) > .btn
+    +border-bottom-radius(0)
+
+  > .btn:not(:first-child),
+  > .btn-group:not(:first-child) > .btn
+    +border-top-radius(0)
+
+// Checkbox and radio options
+//
+// In order to support the browser's form validation feedback, powered by the
+// `required` attribute, we have to "hide" the inputs via `clip`. We cannot use
+// `display: none;` or `visibility: hidden;` as that also hides the popover.
+// Simply visually hiding the inputs via `opacity` would leave them clickable in
+// certain cases which is prevented by using `clip` and `pointer-events`.
+// This way, we ensure a DOM element is visible to position the popover from.
+//
+// See https://github.com/twbs/bootstrap/pull/12794 and
+// https://github.com/twbs/bootstrap/pull/14559 for more information.
+
+.btn-group-toggle
+  > .btn,
+  > .btn-group > .btn
+    margin-bottom: 0
+
+    // Override default `<label>` value
+
+    input[type="radio"],
+    input[type="checkbox"]
+      position: absolute
+      clip: rect(0, 0, 0, 0)
+      pointer-events: none