Don't encourage using ConciseContract or ImplicitContract as ContractFactoryClass

[carver]

What was wrong?

Documentation encourages using ConciseContract and ImplicitContract as a ContractFactoryClass. They are not proper subclasses of Contract, which causes confusion when the API changes (like deploy() is no longer available)

How can it be fixed?

1. Remove references to using these classes as a factory in the documentation
2. Show preferred implementation instead
3. Show using methods on the core contract before wrapping up in these convenience classes
4. Add a deprecation warning when using ConciseContract or ImplicitContract as a factory.

Preferred implementation of ConciseContract, with example core contract methods:

TokenContract = w3.eth.contract(abi=...)

deploy_hash = TokenContract.deploy() 
# wait for deployment transaction to be mined
while True:
    receipt = w3.eth.getTransactionReceipt(deploy_hash)
    if receipt:
        break
    time.sleep(1)

token_contract = TokenContract(receipt['contractAddress'])
token = ConciseContract(token_contract)

 # return my balance
token.balanceOf(MY_ADDR)

 # returns my balance with the core contract (exactly equivalent to previous line)
token_contract.functions.balanceOf(MY_ADDR).call()