Echidna printer: improve constant function detection

[montyly]

Heuristic:

• If view/pure with Solidity >= 0.5 -> Return true
• If it contains assembly -> Return false (Slither doesn't analyze asm)
• Otherwise, check the rules from
  https://solidity.readthedocs.io/en/v0.5.0/contracts.html?highlight=pure#view-functions
• One exception: internal dynamic calls are not correctly handled, so we consider them as non-constant

[montyly]

In addition, this PR adds:

• The type for the constant used. If there is an explicit type conversion (ex : address(0x41)) , the constant is the destination's type (ex : 0x41, address ):

    "constants_used": {
        "Ownable": {
            "transferOwnership(address)": [
                [
                    {
                        "value": 0,
                        "type": "address"
                    }
                ]
            ]
        },

• The constructor of each contract

    "constructors": {
        "Ownable": "Ownable()",
        "BasicToken": "Ownable()",

• The list of functions impacted by a function (if f write a state variable read by g, then f impacts g). The output contains both impacts and is_impacted_by to simplify lookup for third-parties tools.

            "approve(address,uint256)": {
                "impacts": [
                    "transferFrom(address,address,uint256)",
                    "approve(address,uint256)",
                    "allowance(address,address)"
                ],
                "is_impacted_by": [
                    "transferFrom(address,address,uint256)",
                    "approve(address,uint256)",
                ]
            },

[montyly]

I added two additional info:

• have_external_calls: list of functions that call external contracts
• call_a_parameter: if a parameter is directly use as an external call.

Example:

contract C{
    function test() public;
}

contract D{
    C c;

    function f() public{
        c.test();
    }

    function f2(address addr) public{
        C(addr).test();
    }

}

Will give

    "have_external_calls": {
        "D": [
            "f()",
            "f2(address)"
        ]
    },
    "call_a_parameter": {
        "D": [
            {
                "function": "f2(address)",
                "parameter_idx": 0,
                "signature": "test()"
            }
        ]

Note: "signature" will be null for low level calls

[montyly]

Added:

• use_balance: list of functions using balance

contract C{

    function test() public{
        address(this).balance;
    }
}

    "use_balance": {
        "C": [
            "test()"
        ]
    }

Given the number of new features of this printer, the json must be documented.