增加“关闭时最小化到托盘”的设置 (#166)

添加托盘设置，调整主进程代码架构

src/main/rendererEvents/selectDir.js

@@ -0,0 +1,8 @@
+const { mainHandle } = require('../../common/ipc')
+const { dialog } = require('electron')
+
+mainHandle('selectDir', async(event, options) => {
+  if (!global.mainWindow) throw new Error('mainwindow is undefined')
+  return dialog.showOpenDialog(global.mainWindow, options)
+})
+