Persist items to the database

The database that was chosen here is SQLite, because it's dead simple to
setup and more than enough for this project.

Please note that I took some liberty with the assignment. I chose to use
a numeric field for the `id` column of an item. This leverages automatic
creation and incrementation of the id by SQLite itself.

.gitignore

@@ -11,3 +11,4 @@ pom.xml.asc
 /.lsp
 /.nrepl-port
 /.prepl-port
+*.db