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/codemirror-keymap-vim/plugin.info

@@ -4,5 +4,6 @@
 	"description": "Keymap compatible with Vim for CodeMirror",
 	"parent-plugin": "$:/plugins/tiddlywiki/codemirror",
 	"dependents": ["$:/plugins/tiddlywiki/codemirror-search-replace","$:/plugins/tiddlywiki/codemirror-closebrackets"],
-	"list": "readme"
+	"list": "readme",
+	"stability": "STABILITY_2_STABLE"
 }