Move ConversationController to its own file

Encapsulate the global conversation cache collection against accidental
access, avoiding the data-clobbering bug fixed in previous commit.

Also move some one-off program initialization code from panel controller
to background.js

// FREEBIE

js/conversation_controller.js

@@ -0,0 +1,73 @@
+/*global $, Whisper, Backbone, textsecure, extension*/
+/*
+ * vim: ts=4:sw=4:expandtab
+ */
+
+// This script should only be included in background.html
+(function () {
+    'use strict';
+
+    window.Whisper = window.Whisper || {};
+
+    var conversations = new Whisper.ConversationCollection();
+    var inboxCollection = new (Backbone.Collection.extend({
+        initialize: function() {
+            this.on('change:active_at', this.sort);
+            this.on('change:unreadCount', this.updateUnreadCount);
+
+            this.listenTo(conversations, 'add change:active_at', this.addActive);
+        },
+        comparator: function(model) {
+            return -model.get('active_at');
+        },
+        addActive: function(model) {
+            if (model.get('active_at')) {
+                this.add(model);
+            } else {
+                this.remove(model);
+            }
+        },
+        updateUnreadCount: function(model, count) {
+            var prev = model.previous('unreadCount') || 0;
+            if (count < prev) { // decreased
+                var newUnreadCount = storage.get("unreadCount", 0) - (prev - count);
+                setUnreadCount(newUnreadCount);
+                storage.put("unreadCount", newUnreadCount);
+            }
+        }
+    }))();
+
+    window.getInboxCollection = function() {
+        return inboxCollection;
+    };
+
+    window.ConversationController = {
+        get: function(id) {
+            return conversations.get(id);
+        },
+        create: function(attrs) {
+            var conversation = conversations.add(attrs);
+            return conversation;
+        },
+        findOrCreatePrivateById: function(id) {
+            var conversation = conversations.add({ id: id, type: 'private' });
+            return new Promise(function(resolve, reject) {
+                conversation.fetch().then(function() {
+                    resolve(conversation);
+                }).fail(function() {
+                    var saved = conversation.save(); // false or indexedDBRequest
+                    if (saved) {
+                        saved.then(function() {
+                            resolve(conversation);
+                        }).fail(reject);
+                    } else {
+                        reject();
+                    }
+                });
+            });
+        },
+        updateInbox: function() {
+            conversations.fetchActive();
+        }
+    };
+})();