Fixed hasattr overloader method in the web3.ContractEvent, web3.ContractFunction, and web3.ContractCaller classes by implementing a try/except handler that returns False if an exception is raised in the __getattr__ overloader method (since __getattr__ HAS to be called in every __hasattr__ call).

Created two new Exception classes, ‘ABIEventFunctionNotFound’ and ‘ABIFunctionNotFound’, which inherit from both AttributeError and MismatchedABI, and replaced the MismatchedABI raises in ContractEvent, ContractFunction, and ContractCaller with a raise to the created class in the __getattr__ overloader method of the object. (#1594)