CSS files converted to Sass. Some style fixes. Created file with sponsors.

_sass/vendor/bootstrap/mixins/_nav-divider.scss

@@ -0,0 +1,10 @@
+// Horizontal dividers
+//
+// Dividers (basically an hr) within dropdowns and nav lists
+
+@mixin nav-divider($color: #e5e5e5) {
+  height: 1px;
+  margin: (($line-height-computed / 2) - 1) 0;
+  overflow: hidden;
+  background-color: $color;
+}