Some funcitons miss block specification in TokenNetworkRegistry

[pirapira]

In the TokenNetworkRegistry proxy, some getter funcitons miss block specification.

    def settlement_timeout_min(self) -> int:
        """ Returns the minimal settlement timeout for the token network registry. """
        return self.proxy.contract.functions.settlement_timeout_min().call()

    def settlement_timeout_max(self) -> int:
        """ Returns the maximal settlement timeout for the token network registry. """
        return self.proxy.contract.functions.settlement_timeout_max().call()

At least these functions should take to_block argument, like other functions in this class.

[rakanalh]

I fixed this in #4957