Changed bootstrap-sass back to bootstrap (with less). Theme now loads before the preloader is shown.

src/web/stylesheets/vendors/bootstrap.less

@@ -0,0 +1,58 @@
+/**
+ * Bootstrap imports
+ *
+ * @author n1474335 [n1474335@gmail.com]
+ * @copyright Crown Copyright 2017
+ * @license Apache-2.0
+ */
+
+// Core variables and mixins
+@import "~bootstrap/less/variables.less";
+@import "~bootstrap/less/mixins.less";
+
+// Reset and dependencies
+@import "~bootstrap/less/normalize.less";
+@import "~bootstrap/less/print.less";
+// @import "~bootstrap/less/glyphicons.less";
+
+// Core CSS
+@import "~bootstrap/less/scaffolding.less";
+@import "~bootstrap/less/type.less";
+@import "~bootstrap/less/code.less";
+// @import "~bootstrap/less/grid.less";
+@import "~bootstrap/less/tables.less";
+@import "~bootstrap/less/forms.less";
+@import "~bootstrap/less/buttons.less";
+
+// Components
+@import "~bootstrap/less/component-animations.less";
+@import "~bootstrap/less/dropdowns.less";
+@import "~bootstrap/less/button-groups.less";
+@import "~bootstrap/less/input-groups.less";
+@import "~bootstrap/less/navs.less";
+// @import "~bootstrap/less/navbar.less";
+// @import "~bootstrap/less/breadcrumbs.less";
+// @import "~bootstrap/less/pagination.less";
+// @import "~bootstrap/less/pager.less";
+@import "~bootstrap/less/labels.less";
+// @import "~bootstrap/less/badges.less";
+// @import "~bootstrap/less/jumbotron.less";
+// @import "~bootstrap/less/thumbnails.less";
+@import "~bootstrap/less/alerts.less";
+@import "~bootstrap/less/progress-bars.less";
+// @import "~bootstrap/less/media.less";
+@import "~bootstrap/less/list-group.less";
+@import "~bootstrap/less/panels.less";
+// @import "~bootstrap/less/responsive-embed.less";
+// @import "~bootstrap/less/wells.less";
+@import "~bootstrap/less/close.less";
+
+// Components w/ JavaScript
+@import "~bootstrap/less/modals.less";
+@import "~bootstrap/less/tooltip.less";
+@import "~bootstrap/less/popovers.less";
+// @import "~bootstrap/less/carousel.less";
+
+// Utility classes
+@import "~bootstrap/less/utilities.less";
+// @import "~bootstrap/less/responsive-utilities.less";