(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/Features.ts

@@ -0,0 +1,45 @@
+// A product is essentially a list of flags and limits that we may enforce/support.
+export interface Features {
+  vanityDomain?: boolean;   // are user-selected domains allowed (unenforced) (default: true)
+
+  workspaces?: boolean;     // are workspaces shown in web interface (default: true)
+                            // (this was intended as something we can turn off to shut down
+                            // web access to content while leaving access to billing)
+
+  /**
+   * Some optional limits.  Since orgs can change plans, limits will typically be checked
+   * at the point of creation.  E.g. adding someone new to a document, or creating a
+   * new document.  If, after an operation, the limit would be exceeded, that operation
+   * is denied.  That means it is possible to exceed limits if the limits were not in
+   * place when shares/docs were originally being added.  The action that would need
+   * to be taken when infringement is pre-existing is not so obvious.
+   */
+
+  maxSharesPerDoc?: number; // Maximum number of users that can be granted access to a
+                            // particular doc.  Doesn't count users granted access at
+                            // workspace or organization level.  Doesn't count billable
+                            // users if applicable (default: unlimited)
+
+  maxSharesPerDocPerRole?: {[role: string]: number};  // As maxSharesPerDoc, but
+                            // for specific roles.  Roles are named as in app/common/roles.
+                            // Applied independently to maxSharesPerDoc.
+                            // (default: unlimited)
+  maxSharesPerWorkspace?: number;  // Maximum number of users that can be granted access to
+                            // a particular workspace.  Doesn't count users granted access
+                            // at organizational level, or billable users (default: unlimited)
+
+  maxDocsPerOrg?: number;   // Maximum number of documents allowed per org.
+                            // (default: unlimited)
+  maxWorkspacesPerOrg?: number;   // Maximum number of workspaces allowed per org.
+                            // (default: unlimited)
+
+  readOnlyDocs?: boolean;   // if set, docs can only be read, not written.
+}
+
+// Check whether it is possible to add members at the org level.  There's no flag
+// for this right now, it isn't enforced at the API level, it is just a bluff.
+// For now, when maxWorkspacesPerOrg is 1, we should assume members can't be added
+// to org (even though this is not enforced).
+export function canAddOrgMembers(features: Features): boolean {
+  return features.maxWorkspacesPerOrg !== 1;
+}