Listcountis 2281085

see: https://drupal.org/node/2281085
Port "List count comparison (list_count_is)" condition to 8.x

Creates ListCountIs plugin and ListCountIsTest class.

Still need to be able to set default_value, options_list and restriction for the operator parameter.
Missing carriage return at end of file. (You can configure your IDE to automatically add that).