(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/UserConfig.ts

@@ -0,0 +1,31 @@
+/*
+ * Interface for the user's config found in config.json.
+ */
+export interface UserConfig {
+  enableMetrics?: boolean;
+  docListSortBy?: string;
+  docListSortDir?: number;
+  features?: ISupportedFeatures;
+
+  /*
+   * The host serving the untrusted content: on dev environment could be
+   * "http://getgrist.localtest.me". Port is added at runtime and should not be included.
+   */
+  untrustedContentOrigin?: string;
+}
+
+export interface ISupportedFeatures {
+  signin?: boolean;
+  sharing?: boolean;
+  proxy?: boolean;  // If true, Grist will accept login information via http headers
+  // X-Forwarded-User and X-Forwarded-Email.  Set to true only if
+  // Grist is behind a reverse proxy that is managing those headers,
+  // otherwise they could be spoofed.
+  formulaBar?: boolean;
+
+  // Plugin views, REPL, and Validations all need work, but are exposed here to allow existing
+  // tests to continue running. These only affect client-side code.
+  customViewPlugin?: boolean;
+  replTool?: boolean;
+  validationsTool?: boolean;
+}