LIB-43: Use first CD drive letter on Windows as default device

Currently if the default device is used on Windows it tries to access the hardcoded drive "D:". The patch uses the first CD drive instead.

The code is completely stolen from Picard (https://github.com/musicbrainz/picard/blob/master/picard/util/cdrom.py#L33), I just translated it back to C.

EDIT by JonnyJD:
tracked with http://tickets.musicbrainz.org/browse/LIB-43
EDIT by JonnyJD:
updated title to match ticket title