Revert "Set home directory to sdcard instead of app data folder. Fixes #9."

This reverts commit e3219ef80dac72346c65ad9c86f70b73eb2552df.

This change seems to cause problems on Android 2.3 devices, which exit with
error "No home directory found". I can't test this myself, and don't know
if it happens for everyone (ref #9).