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

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

@@ -0,0 +1,159 @@
+// stylelint-disable selector-no-qualifying-type
+
+//
+// Base styles
+//
+
+.input-group
+  position: relative
+  display: flex
+  flex-wrap: wrap
+
+  // For form validation feedback
+  align-items: stretch
+  width: 100%
+
+  > .form-control,
+  > .custom-select,
+  > .custom-file
+    position: relative
+
+    // For focus state's z-index
+    flex: 1 1 auto
+
+    // Add width 1% and flex-basis auto to ensure that button will not wrap out
+    // the column. Applies to IE Edge+ and Firefox. Chrome does not require this.
+    width: 1%
+    margin-bottom: 0
+
+    + .form-control,
+    + .custom-select,
+    + .custom-file
+      margin-left: -$input-border-width
+
+  // Bring the "active" form control to the top of surrounding elements
+  > .form-control:focus,
+  > .custom-select:focus,
+  > .custom-file .custom-file-input:focus ~ .custom-file-label
+    z-index: 3
+
+  > .form-control,
+  > .custom-select
+    &:not(:last-child)
+      +border-right-radius(0)
+
+    &:not(:first-child)
+      +border-left-radius(0)
+
+  // Custom file inputs have more complex markup, thus requiring different
+  // border-radius overrides.
+  > .custom-file
+    display: flex
+    align-items: center
+
+    &:not(:last-child) .custom-file-label,
+    &:not(:last-child) .custom-file-label::after
+      +border-right-radius(0)
+
+    &:not(:first-child) .custom-file-label
+      +border-left-radius(0)
+
+// Prepend and append
+//
+// While it requires one extra layer of HTML for each, dedicated prepend and
+// append elements allow us to 1) be less clever, 2) simplify our selectors, and
+// 3) support HTML5 form validation.
+
+.input-group-prepend,
+.input-group-append
+  display: flex
+
+  // Ensure buttons are always above inputs for more visually pleasing borders.
+  // This isn't needed for `.input-group-text` since it shares the same border-color
+  // as our inputs.
+  .btn
+    position: relative
+    z-index: 2
+
+  .btn + .btn,
+  .btn + .input-group-text,
+  .input-group-text + .input-group-text,
+  .input-group-text + .btn
+    margin-left: -$input-border-width
+
+.input-group-prepend
+  margin-right: -$input-border-width
+
+.input-group-append
+  margin-left: -$input-border-width
+
+// Textual addons
+//
+// Serves as a catch-all element for any text or radio/checkbox input you wish
+// to prepend or append to an input.
+
+.input-group-text
+  display: flex
+  align-items: center
+  padding: $input-padding-y $input-padding-x
+  margin-bottom: 0
+
+  // Allow use of <label> elements by overriding our default margin-bottom
+  font-size: $font-size-base
+
+  // Match inputs
+  font-weight: $font-weight-normal
+  line-height: $input-line-height
+  color: $input-group-addon-color
+  text-align: center
+  white-space: nowrap
+  background-color: $input-group-addon-bg
+  border: $input-border-width solid $input-group-addon-border-color
+
+  +border-radius($input-border-radius)
+
+  // Nuke default margins from checkboxes and radios to vertically center within.
+  input[type="radio"],
+  input[type="checkbox"]
+    margin-top: 0
+
+// Sizing
+//
+// Remix the default form control sizing classes into new ones for easier
+// manipulation.
+
+.input-group-lg > .form-control,
+.input-group-lg > .input-group-prepend > .input-group-text,
+.input-group-lg > .input-group-append > .input-group-text,
+.input-group-lg > .input-group-prepend > .btn,
+.input-group-lg > .input-group-append > .btn
+  @extend .form-control-lg
+
+.input-group-sm > .form-control,
+.input-group-sm > .input-group-prepend > .input-group-text,
+.input-group-sm > .input-group-append > .input-group-text,
+.input-group-sm > .input-group-prepend > .btn,
+.input-group-sm > .input-group-append > .btn
+  @extend .form-control-sm
+
+// Prepend and append rounded corners
+//
+// These rulesets must come after the sizing ones to properly override sm and lg
+// border-radius values when extending. They're more specific than we'd like
+// with the `.input-group >` part, but without it, we cannot override the sizing.
+
+.input-group > .input-group-prepend > .btn,
+.input-group > .input-group-prepend > .input-group-text,
+.input-group > .input-group-append:not(:last-child) > .btn,
+.input-group > .input-group-append:not(:last-child) > .input-group-text,
+.input-group > .input-group-append:last-child > .btn:not(:last-child):not(.dropdown-toggle),
+.input-group > .input-group-append:last-child > .input-group-text:not(:last-child)
+  +border-right-radius(0)
+
+.input-group > .input-group-append > .btn,
+.input-group > .input-group-append > .input-group-text,
+.input-group > .input-group-prepend:not(:first-child) > .btn,
+.input-group > .input-group-prepend:not(:first-child) > .input-group-text,
+.input-group > .input-group-prepend:first-child > .btn:not(:first-child),
+.input-group > .input-group-prepend:first-child > .input-group-text:not(:first-child)
+  +border-left-radius(0)