Add from, to, and userData to TradingStrategy interfaces

[nventuro]

The TradingStrategy interface needs to be augmented with the following fields:

• from: the address that is providing the funds (either directly or via user balance)
• to: the address funds will be sent to (either directly or via user balance)
• userData: arbitrary data provided by the caller of swapBatch

from and to are required to implement certain desired features, such as whitelists. We need for the Vault to pass them so that Trading Strategy can trust these values are correct.

userData opens the door for alternative TS designs, such as only allowing a trade if it is accompanied by a signature from a trusted third party.

[dmf7z]

I would also add the Vault's swap function caller because is does not always equals from.
This is necessary because a Trading Strategy may have to trust the origin of userData that could be a specific Trading Script smart contract which is caller and not always from.

[nventuro]

I'm not sure that's a direction we'd want to go in, why would a TS be restricted to a specific trade script? It seems overly restrictive.

[dmf7z]

TS needs to whitelist one or many trade scripts in case userData needs some level of trust, avoiding any other caller to manipulate it.