use preact for common components across site (#663)

* convert GitHub cards grid from lit-html to preact

* give hit counter the preact treatment

* extract loading spinner component to a shared location

* move *some* loading spinner styles to its JSX

* Update .percy.yml

* pick up images in JS w/ webpack

* pull star/fork icons straight from @primer/octicons

* a bit of cleanup

* check `typeof window !== "undefined"` before rendering

* bump misc. deps

* silence missing license warnings for preact-hooks and preact-compat

* add source-map-loader

* Update loading.js

layouts/_default/projects.html

@@ -3,8 +3,6 @@
   <h1><a href="{{ .Permalink }}">{{ .Title | markdownify }}</a></h1>
 
   <div id="content">
-    <div id="loading-spinner" class="loading"><div></div><div></div><div></div></div>
-
     <div id="github-cards"></div>
 
     <p><a href="https://github.com/jakejarvis?tab=repositories" target="_blank" rel="noopener">View more on GitHub...</a></p>