eth_getProof added to web3-eth package

[nivida]

Description

This PR does add the JSON-RPC method eth_getProof to the web3-eth package.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run test with success and extended the tests if necessary.
• I ran npm run build and tested the resulting file from dist folder in a browser.
• I have tested my code on the live network.

[coveralls]

Coverage increased (+0.04%) to 84.388% when pulling 9434cac on feature-request/getProof into 0109937 on 1.x.

[cgewecke]

LGTM. Just left a question about which block params are valid, but looks good!