Removed "static" from task fn generation

Removed keyword `static` from oil's generation class.  Newly generated tasks will match the [documentation](http://fuelphp.com/docs/general/tasks.html). 

I ran into the issue where I had created an abstract class for my task to extend with parameters in the __construct - my ::run tried to instantiate `new static('a', 'b')` only to have oil error out.  

Because my oil generated static methods I didn't think oil would also instantiate the class.