Persist column settings in the select items dialog. Closes #2224

I didn't check the previous behavior, but I assume it's the same:
This will persist the same settings for the select items dialog in the
classic citation view as well as the add related item dialog.

chrome/content/zotero/selectItemsDialog.js

@@ -61,7 +61,7 @@ var doLoad = async function () {
 		},
 		id: "select-items-dialog",
 		dragAndDrop: false,
-		persistColumns: false,
+		persistColumns: true,
 		columnPicker: true,
 		emptyMessage: Zotero.getString('pane.items.loading')
 	});