Add SALT to db3 wallet

[shargon]

Close #1395

[vncoelho]

Sounds a good idea, @shargon. Some salt, pepper, saffron, etc..

[vncoelho]

@shargon, perhaps this could be optional. What do you think?

I mean, it could even be the default.
However, the option without salt may be of interest of some people.

[shargon]

I think that should be like this by default. In what scenario are you thinking about?

[erikzhang]

I think we can store NEP-2 encrypted keys into db3.

[shargon]

I think we can store NEP-2 encrypted keys into db3.

I will try

[shargon]

I think we can store NEP-2 encrypted keys into db3.

It could be very slow if we have a lot of address encrypted with scrypt

[superboyiii]

Made some tests on this PR
Node:

1. Build and publish neo-cli with reference on neo.
2. Create both json and db3 wallet.
3. Import & export key.
4. Start consensus, make transactions.

Rpc:

1. Invoke openwallet to open wallet by PRC.
2. Invoke listaddress to watch address in wallet.
3. Invoke sendfrom to make transaction.
4. Invoke RpcNep5Tracker for balance and transaction history.

These are based on my local environment which I have already merged this PR into latest master branch.

All tests passed. It works well and compatibly.

[shargon]

Time to merge?

[erikzhang]

I think it is important to use NEP-2 in wallets. We can adjust the settings of SCRYPT to make it be faster.

[shargon]

We can adjust the settings of SCRYPT to make it be faster.

Then we will reduce the security of these wallets.

[erikzhang]

In the worst case, it is as secure as it is today.

[shargon]

Closed in favor of #1444