feature: SUPPORT tvOS

[isaac960623]

Hi @NyaMisty , I just thought your repository is really cool! And it's also very Python-friendly. I have a strong need to download IPA files for tvOS. Would it be possible for you to implement this feature?

After some testing, I suspect it might require modifying the CONFIGURATOR_UA to specify the OS for downloading. Do you have any experience with this?

I tried to set CONFIGURATOR_UA = 'Configurator/2.0 (Apple TV; CPU iPhone OS 9_0 like Mac OS X) AppleWebKit/601.1.46 (KHTML, like Gecko) Mobile/13T534YI' I got the output: {'pings': [], 'metrics': {'dialogId': 'MZApplication.GeneralError', 'message': 'Your request is temporari', 'options': ['OK'], 'actionUrl': ipatool.py:320 'p25-buy.itunes.apple.com/WebObjects/MZFinance.woa/wa/volumeStoreDownloadProduct', 'asnState': 0, 'mtTopic': 'xp_its_main', 'eventType': 'dialog'}, 'failureType': '', 'customerMessage': 'Your request is temporarily unable to be processed.', 'm-allowed': False, 'dialog': {'m-allowed': False, 'message': 'Your request is temporarily unable to be processed.', 'explanation': 'Please try again later.', 'defaultButton': 'ok', 'okButtonString': 'OK', 'initialCheckboxValue': True}, 'cancel-purchase-batch': True}