Filtered Navigation for products should include variation attributes as well

Igor, it seems like the filtered navigation is only built from ProductEntity.getAttributes() which means that it only includes product level attributes. This is an issue for multisku products. For example if we sell cloths and customer wants to search by color or size - these mostly would only be available on ProductSku. I would look into this myself but I am not as familiar with indexing implementation so I hoped you can take a loot at it.

I assume we can simply add new getter ProductEntity.getAllAttributes() that would provide collection of both product and its variants attribute value. However I am not sure what effect this may have of the system as a whole.