Create Facet processors - do not display active items

Problem/Motivation

We should port the "facet filters" from d7 facets + facet api bonus. We're renaming the "facet filters" to "facet processors" for more clarity on what the processors can do.

Remaining tasks

Create a new Processor that implements the \Drupal\facetapi\Processor\BuildProcessorInterface and makes sure active items are not displayed. This can be implemented by removing them from the $results array.

- doesn't need any settings.