electron app:

- add file association for .wacz
- support opening wacz, warc, har files via double-click from os (fixes #24)
- command line: support opening files via command line, as well as specifying --url and --ts
- support cmdline args via 'yarn run start-electron <file> --url <url> --ts <ts>'

webpack.config.js

@@ -35,7 +35,7 @@ const electronMainConfig = (env, argv) => {
         __APP_FILE_SERVE_PREFIX__ : JSON.stringify(APP_FILE_SERVE_PREFIX),
         __HELPER_PROXY__ : JSON.stringify(HELPER_PROXY)
       })
-    ]
+    ],
   }
 };