Restructure background script (#70)

Splits some background script functionality into separate modules:
 - Receiver selector handling is moved to ./SelectorManager.
 - Status bridge handling is moved to ./StatusManager.
 - Menu creation and updates are handled in ./createMenus.
 - Shim creation is handled in ./createShim.

TypedEventTarget allows EventTarget-derived classes to export typed events.

Options type definition is moved to ./lib/options, module assumes more responsibility for update handling and provides a "changed" event.

Private cast._requestSession method allows bypassing receiver selector.

ext/src/receiver_selectors/PopupReceiverSelector.ts

@@ -1,19 +1,23 @@
 "use strict";
 
 import ReceiverSelector, {
-        ReceiverSelectorMediaType } from "./ReceiverSelector";
+        ReceiverSelectorEvents
+      , ReceiverSelectorMediaType } from "./ReceiverSelector";
 
+import { TypedEventTarget } from "../lib/typedEvents";
 import { getWindowCenteredProps } from "../lib/utils";
 import { Message, Receiver } from "../types";
 
 
 export default class PopupReceiverSelector
-        extends EventTarget
+        extends TypedEventTarget<ReceiverSelectorEvents>
         implements ReceiverSelector {
 
     private windowId: number;
     private openerWindowId: number;
+
     private messagePort: browser.runtime.Port;
+    private messagePortDisconnected: boolean;
 
     private receivers: Receiver[];
     private defaultMediaType: ReceiverSelectorMediaType;
@@ -21,6 +25,8 @@ export default class PopupReceiverSelector
 
     private wasReceiverSelected: boolean = false;
 
+    private _isOpen: boolean = false;
+
 
     constructor () {
         super();
@@ -48,6 +54,9 @@ export default class PopupReceiverSelector
 
             this.messagePort = port;
             this.messagePort.onMessage.addListener(this.onPopupMessage);
+            this.messagePort.onDisconnect.addListener(() => {
+                this.messagePortDisconnected = true;
+            });
 
             this.messagePort.postMessage({
                 subject: "popup:/populateReceiverList"
@@ -60,6 +69,9 @@ export default class PopupReceiverSelector
         });
     }
 
+    get isOpen () {
+        return this._isOpen;
+    }
 
     public async open (
             receivers: Receiver[]
@@ -85,6 +97,8 @@ export default class PopupReceiverSelector
           , ...centeredProps
         });
 
+        this._isOpen = true;
+
         this.windowId = popup.id;
         this.openerWindowId = openerWindow.id;
 
@@ -98,8 +112,16 @@ export default class PopupReceiverSelector
                 this.onWindowsFocusChanged);
     }
 
-    public close (): void {
-        browser.windows.remove(this.windowId);
+    public async close (): Promise<void> {
+        if (this.windowId) {
+            await browser.windows.remove(this.windowId);
+        }
+
+        this._isOpen = false;
+
+        if (this.messagePort && !this.messagePortDisconnected) {
+            this.messagePort.disconnect();
+        }
     }