Allow using any provider instead of sticking to HttpProvider

[klntsky]

Allow using any provider instead of sticking to Web3.providers.HttpProvider.

The more generality is the better.

It can be done without breaking the current interface, i. e. constructor could check if the provider given is a string and wrap it into HttpProvider if so, otherwise assume it is a provider object and use it.

[moodysalem]

now that infura has a working websocket endpoint this is higher priority imo deploying to mainnet without websockets via infura is a huge pain because they use a load balancer