(core) move home server into core

Summary: This moves enough server material into core to run a home server.  The data engine is not yet incorporated (though in manual testing it works when ported).

Test Plan: existing tests pass

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2552

app/common/tpromisified.ts

@@ -0,0 +1,25 @@
+// tslint:disable:max-line-length
+// credits: https://stackoverflow.com/questions/49998665/promisified-function-type
+
+// Generic Function definition
+type AnyFunction = (...args: any[]) => any;
+
+// Extracts the type if wrapped by a Promise
+type Unpacked<T> = T extends Promise<infer U> ? U : T;
+
+type PromisifiedFunction<T extends AnyFunction> =
+  T extends () => infer U ? () => Promise<Unpacked<U>> :
+  T extends (a1: infer A1) => infer U ? (a1: A1) => Promise<Unpacked<U>> :
+  T extends (a1: infer A1, a2: infer A2) => infer U ? (a1: A1, a2: A2) => Promise<Unpacked<U>> :
+  T extends (a1: infer A1, a2: infer A2, a3: infer A3) => infer U ? (a1: A1, a2: A2, a3: A3) => Promise<Unpacked<U>> :
+  T extends (a1: infer A1, a2: infer A2, a3: infer A3, a4: infer A4) => infer U ? (a1: A1, a2: A2, a3: A3, a4: A4) => Promise<Unpacked<U>> :
+  // ...
+  T extends (...args: any[]) => infer U ? (...args: any[]) => Promise<Unpacked<U>> : T;
+
+/**
+ * `Promisified<T>` has the same methods as `T` but they all return promises. This is useful when
+ * creating a stub with `grain-rpc` for an api which is synchronous.
+ */
+export type Promisified<T> = {
+  [K in keyof T]: T[K] extends AnyFunction ? PromisifiedFunction<T[K]> : never
+};