Update and integrate `@airswap/validator` package

[dmosites]

Existing Validator: https://github.com/airswap/airswap-protocols/tree/master/source/validator

This contract does pre-flight checks for errors prior to submitting a transaction. To use it on the web app, we'd need to add a checkSwap for the light protocol, either on the existing contract as checkLightSwap or a new contract.

Existing error reasons here: https://github.com/airswap/airswap-protocols/blob/master/source/validator/reasons/en_us.json