Chain Id and Prod/Barn environments improvements

[ramirotw]

1. Make chain id optional in the constructor and default to mainnet
2. Add an optional options param on each API method where we can set the chainId and the env (prod/barn)
3. The API methods should query both prod & barn environments so we abstract them away from the user

[anxolin]

Great to see these changes. I would just add that we should have a way to change the initial defaults from the constructor

This way, we hav two ways of using the SDK

• Always providing the options
• ..or, dapps can change the default network when this one changes

[ramirotw]

3. The API methods should query both prod & barn environments so we abstract them away from the user

@matextrem lets pause the env merging so we can discuss about the pagination