Add plugin stability badges (#8198)

* Initial Commit

* Fix plugin library URL

* Need to set plugin library location for prerelease

* Styling tweaks

* Docs

* Add tests that the core plugins all have a valid stability field

plugins/tiddlywiki/pluginlibrary/plugin.info

@@ -2,5 +2,6 @@
 	"title": "$:/plugins/tiddlywiki/pluginlibrary",
 	"name": "Plugin Library",
 	"description": "Plugin library builder",
-	"list": "readme"
+	"list": "readme",
+	"stability": "STABILITY_2_STABLE"
 }