Add new option -separateInterfaceConstants, which places interface const...

This option places interface constants into their own class, removing the requirement that such an interface be translated to an `abstract class`. For example, the following interface:

```java
public interface Foo {
    const int MyConstant = 3;
    void foo();
}
```

Would now get translated to this:

```csharp
public interface IFoo {
    void Foo();
}

public static class FooConstants {
    public const int MyConstant = 3;
}
```