Use a dedicated repository for swaps

[pietro909]

We currently put all the data into ContractRepository.
This package should instead use its own repository (eg: SwapRepository) to track provider-specific data such as the status, the external ID, request/response, .. and leave the contract data only to the ContractManager.

Once arkade-os/ts-sdk#251 is merged, we can work on this solution and implement a migration for existing data.

• Introduce SwapRepository in next
• Use ContractManager in next
• Bring changes to master