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

static/assets/bootstrap/sass/bootstrap.sass

@@ -0,0 +1,41 @@
+/*!
+ * Bootstrap v4.1.2 (https://getbootstrap.com/)
+ * Copyright 2011-2018 The Bootstrap Authors
+ * Copyright 2011-2018 Twitter, Inc.
+ * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)
+
+@import functions
+@import variables
+@import mixins
+@import root
+@import reboot
+@import type
+@import images
+@import code
+@import grid
+@import tables
+@import forms
+@import buttons
+@import transitions
+@import dropdown
+@import button-group
+@import input-group
+@import custom-forms
+@import nav
+@import navbar
+@import card
+@import breadcrumb
+@import pagination
+@import badge
+@import jumbotron
+@import alert
+@import progress
+@import media
+@import list-group
+@import close
+@import modal
+@import tooltip
+@import popover
+@import carousel
+@import utilities
+@import print