First pass at language plugins for internationalisation

Still quite a few details to work out, but this shows the basic idea of
re-using the theme mechanism to handle language plugins.

Comments and questions welcome.

languages/fr-FR/languageprompt.tid

@@ -0,0 +1,3 @@
+title: $:/lingo/ControlPanel/Language/prompt
+
+Bonjour! Langage courant:

languages/fr-FR/plugin.info

@@ -0,0 +1,8 @@
+{
+	"title": "$:/languages/fr-FR",
+	"name": "fr-FR",
+	"plugin-type": "language",
+	"description": "French (France)",
+	"author": "JeremyRuston",
+	"core-version": ">=5.0.0"
+}