(core) move client code to core

Summary:
This moves all client code to core, and makes minimal fix-ups to
get grist and grist-core to compile correctly.  The client works
in core, but I'm leaving clean-up around the build and bundles to
follow-up.

Test Plan: existing tests pass; server-dev bundle looks sane

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2627

app/client/lib/koArray.d.ts

@@ -0,0 +1,31 @@
+import * as ko from 'knockout';
+
+declare class KoArray<T> {
+  public static syncedKoArray(...args: any[]): any;
+  public peekLength: number;
+  public subscribe: ko.Observable["subscribe"];
+
+  public dispose(): void;
+  public at(index: number): T|null;
+  public all(): T[];
+  public map<T2>(op: (x: T) => T2): KoArray<T2>;
+  public peek(): T[];
+  public getObservable(): ko.Observable<T[]>;
+  public push(...items: T[]): void;
+  public unshift(...items: T[]): void;
+  public assign(newValues: T[]): void;
+  public splice(start: number, optDeleteCount?: number, ...values: T[]): T[];
+  public subscribeForEach(options: {
+    add?: (item: T, index: number, arr: KoArray<T>) => void;
+    remove?: (item: T, arr: KoArray<T>) => void;
+    addDelay?: number;
+  }): ko.Subscription;
+
+  public clampIndex(index: number): number|null;
+  public makeLiveIndex(index?: number): ko.Observable<number> & {setLive(live: boolean): void};
+  public setAutoDisposeValues(): this;
+}
+
+declare function syncedKoArray(...args: any[]): any;
+
+export default function koArray<T>(initialValue?: T[]): KoArray<T>;