Implement basic test environment with matchstick.

[GabrielCamba]

Tests should include:

• Tests that will only run if config env var (see .env file in the root of the repo) is set to mainnet

• Tests that will only run if config env var (see .env file in the root of the repo) is set to gc

• Tests will work as mainnet if tests environments are set - either goerli or rinkeby

• Tests will always test Settlement contract events. It doesn't matter the config file, tests that are testing events on the Settlement contract will always work.

• Write test documentation, for adding a new test

• Write documentation of how to run the tests, placing screenshots.