tabs: add clearURL method, loading tabs clears previous qps

Navigatable has clearURL, which for Search clears "search" qp, and
invites clears "invite" qp. Tab interfaces optionally include
"contentObject: AsTab", and show/hide funcs are passed the contentObject
of the previously loaded tab if one is available, so that they can call
it's clearURL method. This means searches you typed for the accounts tab
won't pop up when switching to activity.

ts/typings/d.ts

@@ -75,6 +75,8 @@ declare interface AsTab {
 declare interface Navigatable {
     // isURL will return whether the given url (or the current page url if not passed) is a valid link to some resource(s) in the class.
     isURL(url?: string): boolean;
+    // clearURL will remove related query params from the current URL. It will likely be called when switching pages.
+    clearURL(): void;
     // navigate will load and focus the resource(s) in the class referenced by the given url (or current page url if not passed).
     navigate(url?: string): void;
 }
@@ -196,14 +198,22 @@ declare interface Tab {
     page: Page;
     tabEl: HTMLDivElement;
     buttonEl: HTMLSpanElement;
-    preFunc?: () => void;
-    postFunc?: () => void;
+    contentObject?: AsTab;
+    preFunc?: (previous?: AsTab) => void;
+    postFunc?: (previous?: AsTab) => void;
 }
 
 declare interface Tabs {
     tabs: Map<string, Tab>;
     pages: Pages;
-    addTab(tabID: string, url: string, preFunc: () => void, postFunc: () => void, unloadFunc: () => void): void;
+    addTab(
+        tabID: string,
+        url: string,
+        contentObject: AsTab | null,
+        preFunc: () => void,
+        postFunc: () => void,
+        unloadFunc: () => void,
+    ): void;
     current: string;
     switch(tabID: string, noRun?: boolean): void;
 }