Windows user_data_dir fix

App.user_data_dir on Windows was returning "~/Application Settings/appname" which is invalid because ~ has no meaning on Windows and because Application Settings folder does not exist (verified not to exist on Windows 7, and I couldn't find mention of it on other versions when googling) I think "Application Data" might have been what was intended, but that is only correct for certain versions.

I changed user_data_dir to return "%APPDATA%/appname" instead. the APPDATA environment variable is valid and correct for this purpose on Windows XP, Vista, 7, and 8 (But NOT on Windows 98, which i figure we don't care about because kivy doesn't support it for other reasons)

This fix is pretty simple, and I think it is correct, but be warned I have not actually tested it yet, because I have not yet successfully built kivy on Windows (make complains "make (e=2): the system cannot find the file specified")