set up base template

- set up top nav
  - auto generate menu from `main`
  - configurable brand (can be hidden or custom, defaults to site title)
  - top nav can be configured to be sticky
- css in top, js at the end of body
- default google analitycs template added to base
- added highlight.js

static/css/hugo-bootswatch-slate.css

@@ -0,0 +1,3 @@
+body.navbar-fixed-top {
+  padding-top: 4.5rem
+}

static/js/hugo-bootswatch-slate.js

@@ -1,2 +1,4 @@
 /* globals hljs */
-if (hljs !== null) hljs.initHighlightingOnLoad()
+;(function () {
+  if (typeof hljs !== 'undefined' && hljs != null) hljs.initHighlightingOnLoad()
+})()