Refactor Horde_Secret.

Refactor Horde_Secret.

Remove Horde_Cipher - simply more maintenance for a class that doesn't
do anything better than can already be done with a PEAR equivalent.

Horde now requires Crypt_Blowfish instead. Crypt_Blowfish has built-in
support for mcrypt, so that optimization still applies. However,
blowfish is an efficient algorithm so the PHP-version is most likely
fine for the vast majority of users (trying to reduce install
complexity).

Horde_Secret:: now has an OO-interface and no longer relies on
Horde_Core.