EthereumProvider and the related refactoring

[nivida]

• Port Web3 to es6.
• Refactor the architecture to more SOLID & clean code.
• Improve provider handling (Web3 should use internally always the same interface).
• Each RPC method should be implemented once.
• Method calls should be delegated with the JS Proxy object instead of adding them on construction.
• Create AbstractWeb3Module class and remove core.packageInit().
• Simplify the internal subscription handling.
• Improve the documentation.
• Fix the log subscription.
• Write unit tests with Jest and move them to the related module folders.
• defaultBlock, defaultAccount, timeoutBlock and confirmationBlock should be configurable for each module over the constructor.
• Refactor ENS module (dependency inversion and not injection, EIP 1577)
• Set up rollup for each module
• Set up eslint & prettier
• Update travis CI
• Improve web3-utils & web3-core-helpers exports

[filips123]

@nivida This PR is now merged. When will new release be published?

[levino]

OMG. I has been merged!! :)

[EddieOne]

How do we use these features?