Improve tests

[andrejrakic]

Leveled up testing of javascript edition

Description

• Made having environment parameters optional to compile contracts and run unit tests. Fixes Remove needing to have a private key environment variable out of the box  #74
• Added NatSpec. Fixes Remove "Hardcoded" warning in RandomNumberConsumer.sol or clarify what it means #55
• Made storage variables that won't change immutable. Saves gas. Fixes Make variable in the constructor immutable #56
• Added mock oracle callbacks to unit tests. Fixes Add mocking return in tests #67, Fixes Unit testing of randomness - callback from mock? #65, Fixes Add callBackWithRandomness in unit tests #54
• Refactored integration tests to listen for specific on-chain events instead of waiting for js timeout. Fixes Add mocking return in tests #67, Fixes FEAT: Change integration tests sleep to listen specifically to events #59

Related issues

Related issues are:

• Remove needing to have a private key environment variable out of the box  #74
• Remove "Hardcoded" warning in RandomNumberConsumer.sol or clarify what it means #55
• Make variable in the constructor immutable #56
• Unit testing of randomness - callback from mock? #65
• Add callBackWithRandomness in unit tests #54
• Add mocking return in tests #67
• FEAT: Change integration tests sleep to listen specifically to events #59

[andrejrakic]

Closing this because of #80 and #87