More stabilised version.

1. icon images are added in resource folder
2. MainView is changed for web view: now system checks when url is changed on the web view.
3. When quit button is pressed on AVN/ECU Updater, app closes and saves the current url as well.
4. Fixed minor bugs when user goes to home with 'Home Screen Button', the app doesn't die anymore.
5. NSString is now saved in setBackURL method instead of NSURL: NSURL doesn't work properly when used
    in NSUserDefaults.

What to change on next commit
1. When tapped for a long time, web view shows irrelevant default options; we need to disable them.
2. Any other minor fixes after examinations.