Support nullable members should be optional

[enkelmedia]

TypeScript has something called "Optional Members":

export interface Poco {
name: string;
birthdate? : Date; // Optional
}

If my poco has a nullable member

public class Poco {
   public string Name {get;set;}
   public DateTime? Birthdate {get;set}
}

The current implementation would not make the nullable member optional.

[enkelmedia]

PR: https://github.com/pankleks/TypeScriptBuilder/pull/29