Checking and handling for deterministic vs non-deterministic wallet

Checking and handling for deterministic vs non-deterministic wallet

simple_wallet::seed()

 - Check that wallet is deterministic.

simple_wallet::new_wallet()

 - Prompt for seed language only if it's a non-deterministic wallet,
   along with previous conditions.

simple_wallet::open_wallet()

 - Fixed check for deterministic wallet (flag based on command line
   non-deterministic argument was used before, but it's inapplicable to
   opening an existing wallet).

 - As with deterministic wallet, non-deterministic also included to be
   rewritten to new JSON format file. That's what's done for newly
   generated non-deterministic wallets, so old versions should be
   updated to same format.