Rearchitect the Shell to have a components system

Components are pieces of the shell code that can be added/removed
at runtime, like extension, but are tied more directly to a session
mode. The session polkit agent, the network agent, autorun/automount,
are all components, keyring, recorder and telepathy client are all
now copmonents.

https://bugzilla.gnome.org/show_bug.cgi?id=683156

js/ui/components/__init__.js

@@ -0,0 +1,61 @@
+
+const Lang = imports.lang;
+const Main = imports.ui.main;
+
+const ComponentManager = new Lang.Class({
+    Name: 'ComponentManager',
+
+    _init: function() {
+        this._allComponents = {};
+        this._enabledComponents = [];
+
+        Main.sessionMode.connect('updated', Lang.bind(this, this._sessionUpdated));
+        this._sessionUpdated();
+    },
+
+    _sessionUpdated: function() {
+        let newEnabledComponents = Main.sessionMode.components;
+
+        newEnabledComponents.filter(Lang.bind(this, function(name) {
+            return this._enabledComponents.indexOf(name) == -1;
+        })).forEach(Lang.bind(this, function(name) {
+            this._enableComponent(name);
+        }));
+
+        this._enabledComponents.filter(Lang.bind(this, function(name) {
+            return newEnabledComponents.indexOf(name) == -1;
+        })).forEach(Lang.bind(this, function(name) {
+            this._disableComponent(name);
+        }));
+
+        this._enabledComponents = newEnabledComponents;
+    },
+
+    _importComponent: function(name) {
+        let module = imports.ui.components[name];
+        return module.Component;
+    },
+
+    _ensureComponent: function(name) {
+        let component = this._allComponents[name];
+        if (component)
+            return component;
+
+        let constructor = this._importComponent(name);
+        component = new constructor();
+        this._allComponents[name] = component;
+        return component;
+    },
+
+    _enableComponent: function(name) {
+        let component = this._ensureComponent(name);
+        component.enable();
+    },
+
+    _disableComponent: function(name) {
+        let component = this._allComponents[name];
+        if (component == null)
+            return;
+        component.disable();
+    }
+});