Upgrade to FontAwesome 5 (take two) (#6673)

* Add missing icons to set

* Revert FA5 revert

 This reverts commit 42572ff

* use new SVG syntax in locales

* Noscript page changes (remove login button, center "powered by" footer text)

* Cast wider net for SVG icons in settings

- include any _icon setting for SVG registry (offers better support for plugin settings)

- let themes store multiple pipe-delimited icons in a setting

- also replaces broken onebox image icon with SVG reference in cooked post processor

* interpolate icons in locales

* Fix composer whisper icon alignment

* Add support for stacked icons

* SECURITY: enforce hostname to match discourse hostname

This ensures that the hostname rails uses for various helpers always matches
the Discourse hostname

* load SVG sprite with pre-initializers

* FIX: enable caching on SVG sprites

* PERF: use JSONP for SVG sprites so they are served from CDN

This avoids needing to deal with CORS for loading of the SVG

Note, added the svg- prefix to the filename so we can quickly tell in
dev tools what the file is

* Add missing SVG sprite JSONP script to CSP

* Upgrade to FA 5.5.0

* Add support for all FA4.7 icons

- adds complete frontend and backend for renamed FA4.7 icons

- improves performance of SvgSprite.bundle and SvgSprite.all_icons

* Fix group avatar flair preview

- adds an endpoint at /svg-sprites/search/:keyword

- adds frontend ajax call that pulls icon in avatar flair preview even when it is not in subset

* Remove FA 4.7 font files

package.json

@@ -6,6 +6,7 @@
   "author": "Discourse",
   "license": "MIT",
   "dependencies": {
+    "@fortawesome/fontawesome-free": "5.5.0",
     "ace-builds": "1.4.1",
     "bootbox": "3.2.0",
     "chart.js": "2.7.2",
@@ -15,9 +16,9 @@
     "jquery": "3.3.1",
     "jquery-color": "1.0.0",
     "jquery-resize": "https://github.com/cowboy/jquery-resize/",
+    "jquery-tags-input": "1.3.5",
     "jquery.autoellipsis": "https://github.com/pvdspek/jquery.autoellipsis",
     "jquery.cookie": "1.4.1",
-    "jquery-tags-input": "1.3.5",
     "magnific-popup": "1.1.0",
     "markdown-it": "8.4.1",
     "mousetrap": "https://github.com/discourse/mousetrap#firefox-alt-key",