feat(forge): Better deployment

Add the ability for forge to use a solidity file to create a contract on mainnet and arbitrary deploy scripts by adding a cheatcode. You could do something like:

```solidity
contract t {
    function deployMyContract() {
        uint256 input1 = dep.someFunc();
        vm.mainnetDeploy();
        MyContract t = new MyContract(input1);
    }
}