Send outgoing messages via Outbox folder: Closes #4569

Squashed commit of many patches that merged Eric's outbox patch
as well as additional changes to upgrade the database rather than
require it be wiped and some refactoring suggested by the Outbox
implementation.  Also updated Outbox to be fully atomic via
Transactions.

sql/Version-003.sql

@@ -0,0 +1,13 @@
+
+--
+-- SmtpOutboxTable
+--
+
+CREATE TABLE SmtpOutboxTable (
+    id INTEGER PRIMARY KEY,
+    ordering INTEGER,
+    message TEXT
+);
+
+CREATE INDEX SmtpOutboxOrderingIndex ON SmtpOutboxTable(ordering ASC);
+