Feature/multi send

[AngelicaFulcher]

Fixes #704

🚀 Description

MultiSendToken contract allows the transfer of specific amounts to multiple accounts. Implemented as an extra functionality of a StandardToken.

• 📘 I've reviewed the OpenZeppelin Contributor Guidelines
• ✅ I've added tests where applicable to test my new functionality.
• 📖 I've made sure that my contracts are well-documented.
• 🎨 I've run the JS/Solidity linters and fixed any issues (npm run lint:all:fix).

[sheluchin]

What about allowing users to multisend ETH as well as ERC20 tokens?

[SCBuergel]

@sheluchin I'd suggest using e.g. wrapped ETH to multi-send Ether.

The idea here is that you could derive some custom token from this MultiSendToken in order to have the functionality, that's something very token-specific.

[sheluchin]

I understand the idea here but still think a broader approach would be better. There's obviously a need for a reference multisend contract that people can use. I don't entirely agree that it always needs to be coupled to StandardToken, as there may be users who want to multisend many different types of existing ERC20 tokens and there's no reason code like this can't be used generically.

W-ETH would work but it's somewhat inconvenient for both the sender and the receiver.

https://github.com/Alonski/MultiSendEthereum/blob/master/contracts/MultiSend.sol may be of interest to anyone reading this PR as it handles multisending ERC20 tokens as well as ETH.

In any case, thank you @AngelicaFulcher for posting this PR in the first place.

[rstormsf]

mutlisend eth is different than erc20 multisend.
Also, I wouldn't agree multisendToken needs to inherit from StandardToken

Check out similar Dapp:
https://rstormsf.github.io/multisender/#/

[nventuro]

Closing due to staleness. I also agree with the statement that a more generic solution would be preferred, since these can be easily added ad-hoc by users when required.