Add index to Wallet type

[vshab]

Description

Currently there is no way to access accounts in wallet. This change make it possible.

web3.eth.accounts.wallet[0].address;

Type of change

• Bug fix
• Enhancement

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 warnings.
• I have updated or added types for all modules I've changed
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run test in the root folder with success and extended the tests if necessary.
• I ran npm run build in the root folder and tested it in the browser and with node.
• I ran npm run dtslint in the root folder and tested that all my types are correct
• I have tested my code on an ethereum test network.

[coveralls]

Coverage remained the same at 95.4% when pulling 8ae4bb3 on vshab:fix/add-wallet-index into 9f3c712 on ethereum:1.0.

[coveralls]

Coverage remained the same at 95.4% when pulling 8ae4bb3 on vshab:fix/add-wallet-index into 9f3c712 on ethereum:1.0.

[joshstevens19]

Looks good to me, thanks for the PR 👍 @nivida can you merge please.