Database access: remove completely from R

[devilgate]

Following on from the work we did in #35 (and see comments on its PR, #47), I would like to eventually move all the database access into Java, so we could do it via JDBC, and completely remove the dependence on ODBC. That removal wasn't possible in the earlier work because of a problem with the SQL Server JDBC driver under certain versions.

I looked into this approach while I was working on #35, but the way the DB was used in the R code was too convoluted, and my R knowledge wasn't up to it. At some point in the future, I'd like to take the time to sort all that out, but I'm marking this as "nice to have," because what we have works, so this change is far from essential.