Update devDependencies, gems and lots of cleanup/build fixes.

* switch to grunt-postcss and autoprefixer directly; this is the recommended way.
* uglify: specify `ie8` for compatibility
* specify `cascade:false` for autoprefixer
* specify `ieCompat` for less
* drop grunt-contrib-compress since it doesn't work with Node.js 10.x
* remove grunt-contrib-htmlmin to match the v4 docs
* clean up Gruntfile.js
* clean up .travis.yml and backport changes from v4
* build ie10-viewport-bug-workaround.less since it's used in examples
* move shrinkwrap to root
* bs-commonjs-generator.js: Use `path.posix`
* remove .hound.yml
* remove references to no longer used PR bots
* backport and adapt the sri generation script from v4

docs/_includes/footer.html

@@ -37,7 +37,7 @@
   <script src="{{ site.baseurl }}/assets/js/docs.min.js"></script>
 {% else %}
   {% for file in site.data.configBridge.paths.docsJs %}
-  <script src="{{ file }}"></script>
+  <script src="{{ file | replace_first: '..', site.baseurl }}"></script>
   {% endfor %}
 {% endif %}
 
@@ -47,7 +47,7 @@
     <script src="{{ site.baseurl }}/assets/js/customize.min.js"></script>
   {% else %}
     {% for file in site.data.configBridge.paths.customizerJs %}
-    <script src="{{ file }}"></script>
+    <script src="{{ file | replace_first: '..', site.baseurl }}"></script>
     {% endfor %}
   {% endif %}
 {% endif %}