Static Deploy to Github Pages (#73)

Addresses #58 , "As a member of the public, I want to see J40's website live on the internet, so that I know it's real!" - hosting on github pages for now as a temporary measure. This fix does NOT: 1) add .gov domain hosting, or 2) post to the geoplatform s3 bucket. This will need to happen in a subsequent fix. 

The changes made specifically to enable this for now:
* Adding github action to build, test, and deploy on pushes to client/
* Adding path prefix to build gh-pages at https://usds.github.io/justice40-tool/
* (Temporarily) pointing to fix branch for trussworks to enable SSR building
* Removing the workaround for the above bug in gatsby-node.js
* Setting build target to be 14.x due to version number limitations
* Adding gh-pages dependency, deploy action for manual deploy
* Force renaming J40header -> J40Header and J40footer -> J40Footer due to Linux case sensitivity

client/gatsby-config.js

@@ -12,6 +12,7 @@ module.exports = {
   siteMetadata: {
     title: "Justice40",
   },
+  pathPrefix: "/justice40-tool",
   plugins: [
     {
       resolve: 'gatsby-plugin-sass',

client/gatsby-node.js

@@ -6,16 +6,4 @@ exports.onCreateWebpackConfig = ({ stage, loaders, actions }) => {
   actions.setWebpackConfig({
     devtool: 'eval-source-map',
   });  
-  if (stage === "build-html" || stage === "develop-html") {
-      actions.setWebpackConfig({
-        module: {
-          rules: [
-            {
-              test: /@trussworks\/react-uswds/,
-              use: loaders.null(),
-            },
-          ],
-        }
-      })
-    }
-  }
+}

client/package.json

@@ -10,9 +10,10 @@
   "scripts": {
     "develop": "gatsby develop",
     "start": "gatsby develop",
-    "build": "gatsby build",
+    "build": "gatsby build --prefix-paths",
     "serve": "gatsby serve",
     "clean": "gatsby clean",
+    "deploy": "gatsby build --prefix-paths && gh-pages -d public",
     "intl:extract": "formatjs extract 'src/(pages|components)/*.tsx' --out-file src/intl/en.json",
     "intl:compile": "formatjs compile src/intl/en.json --ast --out-file compiled-lang/en.json"
   },
@@ -24,11 +25,12 @@
     "gatsby-cli": "^3.5.0",
     "gatsby-plugin-intl": "^0.3.3",
     "gatsby-plugin-sass": "^4.5.0",
+    "gh-pages": "^3.2.0",
     "sass": "^1.33.0",
     "sass-loader": "^11.1.1"
   },
   "dependencies": {
-    "@trussworks/react-uswds": "^1.17.0",
+    "@trussworks/react-uswds": "trussworks/react-uswds#kh-serverside-rendering-fix-1250",
     "gatsby": "^3.4.1",
     "react": "^17.0.1",
     "react-dom": "^17.0.1"