(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/TabularDiff.ts

@@ -0,0 +1,31 @@
+/**
+ *
+ * Types for use when summarizing differences between versions of a table, with the
+ * diff itself presented in tabular form.
+ *
+ */
+
+
+/**
+ * Pairs of before/after values of cells. Values, when present, are nested in a trivial
+ * list since they can be literally anything - null, undefined, etc.  Otherwise they
+ * are either null, meaning non-existent, or "?", meaning unknown.  Non-existent values
+ * appear prior to a table/column being created, or after it has been destroyed.
+ * Unknown values appear when they are omitted from summaries of bulk actions, and those
+ * summaries are then merged with others.
+ */
+export type CellDelta = [[any]|"?"|null, [any]|"?"|null];
+
+/** a special column indicating what changes happened on row (addition, update, removal) */
+export type RowChangeType = string;
+
+/** differences for an individual table */
+export interface TabularDiff {
+  header: string[];  /** labels for columns */
+  cells: Array<[RowChangeType, number, CellDelta[]]>;  // "number" is rowId
+}
+
+/** differences for a collection of tables */
+export interface TabularDiffs {
+  [tableId: string]: TabularDiff;
+}