Use a default SMTP port of 25 (Issue #109)

I noticed issue #109 was fairly straightforward, and probably low-hanging fruit.

The most important change in this pull request is to the actual ``CREATE TABLE`` statement that assigns a default value of 25 for SMTP port. However, I included some extra logic for backwards compatibility so that settings pulled from an existing database will be updated with a default value. Tests to confirm this are included.

Thanks!