Replace default autoUpdater notification on a dialog window with notification and the possible options

[kashamalasha]

electron-updater helper uses the system's built-in notification after finding a new version in the latest files on Github. On Linux, the application freezes during try to notify a user about the update is found if the libnotify-bin doesn't set up correctly. It should work better if the application will handle the 'update-available' event instead of autoUpdater.checkForUpdatesAndNotify() call.