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

static/assets/bootstrap/sass/_root.sass

@@ -0,0 +1,15 @@
+\:root
+  // Custom variable values only support SassScript inside `#{}`.
+  @each $color, $value in $colors
+    --#{$color}: #{$value}
+
+  @each $color, $value in $theme-colors
+    --#{$color}: #{$value}
+
+  @each $bp, $value in $grid-breakpoints
+    --breakpoint-#{$bp}: #{$value}
+
+  // Use `inspect` for lists so that quoted items keep the quotes.
+  // See https://github.com/sass/sass/issues/2383#issuecomment-336349172
+  --font-family-sans-serif: #{inspect($font-family-sans-serif)}
+  --font-family-monospace: #{inspect($font-family-monospace)}