Encrypt password file

Use OpenSSL to encrypt and decrypt saved passwords.

Fix the password container format so that one can have multiple user
password combinations for one URL.
Prompt for password

Remove hard coded seed used for password generation. Ask user for
password and use it as the seed. Asked password is also used for
encrypting and decrypting the password storage file.
Prevent overwriting of password storage file with new password
Change default behaviour to list passwords

On default we now list all passwords matching the first argument
pattern. If no match is found add password as earlier.