Dynamic loading/unloading of plugins (#4259)

* First pass at dynamic loading/unloading

* Show warning for changes to plugins containing JS modules

* Use $:/config/RegisterPluginType/* for configuring whether a plugin type is automatically registered

Where "registered" means "the constituent shadows are loaded".

* Fix the info plugin

The previous mechanism re-read all plugin info during startup

* Don't prettify JSON in the plugin library

* Indicate in plugin library whether a plugin requires reloading

* Display the highlighted plugin name in the plugin chooser

And if there's no name field fall back to the part of the title after the final slash.

core/modules/commands/makelibrary.js

@@ -59,7 +59,7 @@ Command.prototype.execute = function() {
 		title: upgradeLibraryTitle,
 		type: "application/json",
 		"plugin-type": "library",
-		"text": JSON.stringify({tiddlers: tiddlers},null,$tw.config.preferences.jsonSpaces)
+		"text": JSON.stringify({tiddlers: tiddlers})
 	};
 	wiki.addTiddler(new $tw.Tiddler(pluginFields));
 	return null;