Extract properties from IExpression to separate interface

[sys27]

public interface IExpression
{
    // ...
    int MinParameters { get; }
    int MaxParameters { get; }
    int ParametersCount { get; }
    // ...
}

Probably, these properties should be a part of separate interface (e.g. IFunctionExpression), because these parameter are only used for validation of parameters from FuntionToken.