move config.startTime to app.startTime

This also captures the true start time since it runs before any
require() calls, so the time to require() will be taken into account.

main/index.js

@@ -1,9 +1,14 @@
+var startTime = Date.now()
+
 var electron = require('electron')
+var ipc = require('./ipc')
 var menu = require('./menu')
 var windows = require('./windows')
-var ipc = require('./ipc')
+
 var app = electron.app
 
+app.startTime = startTime
+
 app.on('open-file', onOpen)
 app.on('open-url', onOpen)