accounts: fix infinite scroll over-loading, use scrollend+polyfill

calculation for number of rows to be drawn was wrong, fixed now. To
compensate for overshooting with fast scrolling, speed is calculated
using previous scrollY in rows/scroll, and used to render more rows.
Also, the "scrollend" event is used to load more at the end of a scroll
always. Since this isn't available on safari/webkit(2gtk), a polyfill
has been added.

ts/modules/tabs.ts

@@ -24,7 +24,7 @@ export class Tabs implements Tabs {
         });
     }
 
-    addTab = (tabID: string, url: string, preFunc = () => void {}, postFunc = () => void {},) => {
+    addTab = (tabID: string, url: string, preFunc = () => void {}, postFunc = () => void {}, unloadFunc = () => void {}) => {
         let tab: Tab = {
             page: null,
             tabEl: document.getElementById("tab-" + tabID) as HTMLDivElement,
@@ -50,6 +50,7 @@ export class Tabs implements Tabs {
                 tab.buttonEl.classList.remove("active");
                 tab.buttonEl.classList.remove("~urge");
                 tab.tabEl.classList.add("unfocused");
+                if (unloadFunc) unloadFunc();
                 return true;
             },
             shouldSkip: () => false,