[win32] fix running XBMC with custom home directory

The first commit fixes usage of APP_HOME because XBMC_HOME doesn't exist anymore.
@Memphiz: I also noticed that there are still a few OSX-related files/scripts containing XBMC_HOME.

The second commit renames XBMC_PROFILE_USERDATA (win32 only) to APP_PROFILE_USERDATA but it's only set and never read so not sure why it's there in the first place.