Adds nonce to a tx, adds yarn build:link support, updates functions for API calls, refactoring

[dan437]

Description

This PR:

• Adds nonce to a tx during the getUnsignedTransactionsAndEstimates call
• Adds yarn build:link support and documentation. This way we can easily make changes in the controller and see them e.g. in the MM extension
• Updates functions for API calls (renaming, returned values, types, use our new transaction APIs server URL)
• Adds 'Content-Type': 'application/json' for each API call
• Turns off "require-atomic-updates" in ESLint
• Updates and refactor unit tests, so they are all green now and meet the Jest threshold

[wachunei]

LGTM!