Validator manager contract utils

[mhchia]

A simple version of the contract utils of basic sharding v1 with a simple tester test(), without unit-tests.

Main functions

call_deposit(state, validator_manager_addr, sender_privkey, value, validation_code_addr, return_addr) returns validator_index, transaction

call_withdraw(state, validator_manager_addr, sender_privkey, validator_index, signature) returns success, transaction

call_sample(state, validator_manager_addr, block_number, shard_id, sig_index) returns validation_code_addr

call_validation_code(state, validation_code_addr, msg_hash, signature) returns success

TODO

• Be more clear with the structure of State
• Be sure about startgas and gaslimit
• Be sure about what will affect and happen in vm.Message, ...
• Finish unit-tests and put them into files in sharding/tests

[hwwhww]

I advise moving the tests to sharding/tests/test_contract_utils.py, so we can test the entire project by pytest sharding/tests command.

[mhchia]

This PR is contained by the PR #6