Issue #1496654 by alexpott, tobiasb: convert aggregator admin form to...

Issue #1496654 by alexpott, tobiasb: convert aggregator admin form to configuration system -- add file missed by previous commit

core/modules/aggregator/config/aggregator.settings.yml

+fetcher: aggregator
+parser: aggregator
+processors:
+    - aggregator
+items:
+    allowed_html: '<a> <b> <br> <dd> <dl> <dt> <em> <i> <li> <ol> <p> <strong> <u> <ul>'
+    teaser_length: '600'
+    expire: '9676800'
+source:
+    list_max: '3'
+    category_selector: checkboxes