(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/emails.ts

@@ -0,0 +1,43 @@
+/**
+ *
+ * Utilities related to email normalization.  Currently
+ * trivial, but could potentially need special per-domain
+ * rules in future.
+ *
+ * Email addresses are a bit slippery.  Domain names are
+ * case insensitive, but user names may or may not be,
+ * depending on the mail server handling the domain.
+ * Other special treatment of user names may also be in
+ * place for particular domains (periods, plus sign, etc).
+ *
+ * We treat emails as case-insensitive for the purposes
+ * of determining equality of emails, and indexing users
+ * by email address.
+ *
+ */
+
+/**
+ *
+ * Convert the supplied email address to a normalized form
+ * that we will use for indexing and equality tests.
+ * Many possible email addresses could map to the same
+ * normalized result; as far as we are concerned those
+ * addresses are equivalent.
+ *
+ * The normalization we do is a simple lowercase.  This
+ * means we won't be able to treat both Jane@x.y and
+ * jane@x.y as separate email addresses, even through
+ * they may in fact be separate mailboxes on x.y.
+ *
+ * The normalized email is not something we should show
+ * the user in the UI, but is rather for internal purposes.
+ *
+ * The original non-normalized email is called a
+ * "display email" to distinguish it from a "normalized
+ * email"
+ *
+ */
+export function normalizeEmail(displayEmail: string): string {
+  // We take the lower case, without use of locale.
+  return displayEmail.toLowerCase();
+}