Incompatible return types for 4.x implementations

[nazarhussain]

While migrating truffle came across a few changes which are required to make web3@4x compatible with a lot of projects our there.

Here is the the list of individual changes:

1. web3.eth.getTransaction should always return transaction or throw. Should not have return type of undefined.
2. web3.eth.getTransactionReceipt should always return receipt or throw. Should not have return type of undefined.
3. TransactionReceipt property address should not be optional.

[mconnelly8]

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