admin: tab system improvement, search: ?search qp

tab content classes (e.g. settingsList, activityList)
can implement "AsTab", "Navigatable" and or "PageEventBindable",
the first giving them a tab name, a subpath and a reloader function,
the second an "isURL" and "navigate" function for loading resources,
the last giving them bind/unbindPageEvent methods. These are looped
through in ts/admin.ts still crudely, maybe tabs.ts could accept "AsTab"
implementers directly.

"Search" class now has a ?search query param which just encodes the
search box content, set when you perform a server search (hit enter or
press the button). ?user queries from the accounts or activity tab will
be converted to this form on loading.

ts/modules/tabs.ts

@@ -1,5 +1,13 @@
 import { PageManager, Page } from "../modules/pages.js";
 
+export function isPageEventBindable(object: any): object is PageEventBindable {
+    return "bindPageEvents" in object;
+}
+
+export function isNavigatable(object: any): object is Navigatable {
+    return "isURL" in object && "navigate" in object;
+}
+
 export interface Tab {
     page: Page;
     tabEl: HTMLDivElement;