Encode scripts in base64

[roman-khimov]

Summary or problem description
neo-project/neo#1199 changed VM script JSON representation for contract states, transactions and some other structures. But in modules we still have invokescript RPC method accepting hex-encoded scripts and all invoke* methods returning hex-encoded data in the script field. It all works just fine, but still it seems to be a little inconsistent, one representation for all cases is more convenient.

Do you have any solution you want to propose?
Change invoke* methods to work with base64-encoded scripts, both for input and output.

It may also be extended to non-verbose block/header/transaction/storage item getters, but that's more invasive and questionable.

Where in the software does this update applies to?

• Plugins