(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/ActionGroup.ts

@@ -0,0 +1,19 @@
+import {ActionSummary} from 'app/common/ActionSummary';
+
+/** This is the action representation the client works with. */
+export interface ActionGroup {
+  actionNum: number;
+  actionHash: string;
+  desc?: string;
+  actionSummary: ActionSummary;
+  fromSelf: boolean;
+  linkId: number;
+  otherId: number;
+  time: number;
+  user: string;
+  rowIdHint: number;      // If non-zero, this is a rowId that would be a good place to put
+                          // the cursor after an undo.
+  primaryAction: string;  // The name of the first user action in the ActionGroup.
+  isUndo: boolean;        // True if the first user action is ApplyUndoActions.
+  internal: boolean;      // True if it is inappropriate to log/undo the action.
+}