support other SQLite wrappers, and various hooks needed by grist-static (#516)

app/client/models/AppModel.ts

@@ -1,4 +1,5 @@
 import {BehavioralPromptsManager} from 'app/client/components/BehavioralPromptsManager';
+import {hooks} from 'app/client/Hooks';
 import {get as getBrowserGlobals} from 'app/client/lib/browserGlobals';
 import {makeT} from 'app/client/lib/localization';
 import {sessionStorageObs} from 'app/client/lib/localStorageObs';
@@ -131,7 +132,7 @@ export class TopAppModelImpl extends Disposable implements TopAppModel {
 
   constructor(
     window: {gristConfig?: GristLoadConfig},
-    public readonly api: UserAPI = new UserAPIImpl(getHomeUrl()),
+    public readonly api: UserAPI = newUserAPIImpl(),
   ) {
     super();
     setErrorNotifier(this.notifier);
@@ -436,6 +437,12 @@ export function getHomeUrl(): string {
   return (gristConfig && gristConfig.homeUrl) || `${protocol}//${host}`;
 }
 
+export function newUserAPIImpl(): UserAPIImpl {
+  return new UserAPIImpl(getHomeUrl(), {
+    fetch: hooks.fetch,
+  });
+}
+
 export function getOrgNameOrGuest(org: Organization|null, user: FullUser|null) {
   if (!org) { return ''; }
   if (user && user.anonymous && org.owner && org.owner.id === user.id) {

app/client/models/gristUrlState.ts

@@ -23,6 +23,7 @@
  * Note that the form of URLs depends on the settings in window.gristConfig object.
  */
 import {unsavedChanges} from 'app/client/components/UnsavedChanges';
+import {hooks} from 'app/client/Hooks';
 import {UrlState} from 'app/client/lib/UrlState';
 import {decodeUrl, encodeUrl, getSlugIfNeeded, GristLoadConfig, IGristUrlState,
         parseFirstUrlPart} from 'app/common/gristUrls';
@@ -134,7 +135,9 @@ export class UrlStateImpl {
    */
   public encodeUrl(state: IGristUrlState, baseLocation: Location | URL): string {
     const gristConfig = this._window.gristConfig || {};
-    return encodeUrl(gristConfig, state, baseLocation);
+    return encodeUrl(gristConfig, state, baseLocation, {
+      tweaks: hooks.urlTweaks,
+    });
   }
 
   /**
@@ -142,7 +145,9 @@ export class UrlStateImpl {
    */
   public decodeUrl(location: Location | URL): IGristUrlState {
     const gristConfig = this._window.gristConfig || {};
-    return decodeUrl(gristConfig, location);
+    return decodeUrl(gristConfig, location, {
+      tweaks: hooks.urlTweaks,
+    });
   }
 
   /**