Refactoring Combustibles.java and Combustible.java

Centralice toda la logica de combustibles en Combustibles.java, y refactorice Combustible.java.

De Combustibles.java he eliminado la funcion de buscar el historico de precios por el momento ya que la pagina de la SEIC con los historicos no incluye la fecha de publicacion de los mismos en un formato estandar y facilmente parseable.
Well I guess whatever floats your boat.

My personal philosophy is that if two types are tightly bound to each other, such as these, then one is a good candidate to be declared inside the other, otherwise both should be placed in their own package.

What do you think?