pgup/pgdown hotkey normalization:

- pgup/pgdown without modifier scroll headline buffer
- shift+pgup/pgdown work similarly to shift+up/down but operating on pages

js/Headlines.js

@@ -1381,6 +1381,12 @@ define(["dojo/_base/declare"], function (declare) {
 
 			}
 		},
+		scrollByPages: function (offset) {
+			const hi = $("headlines-frame");
+			if (hi) {
+				hi.scrollTop += hi.offsetHeight * offset * 0.9;
+			}
+		},
 		initHeadlinesMenu: function () {
 			if (!dijit.byId("headlinesMenu")) {