Create objects from scripting

[tobbi]

Fixes #2445

[tobbi]

Actually, as for # 366 this only fixes the first two things.

[Vankata453]

Wouldn't this be better suited for the Sector scripting class? That way it'd be accessible for the current sector from sector.settings.

[tobbi]

Default arguments will not be possible anymore then:

function add_object(class_name, name, posX, posY, direction = "left", data = "")
{
  Level_add_object(class_name, name, posX, posY, direction, data);
}