Fix tests subdirectory for ResourceT in Persistent types (SQL/postgres version)

The *tests* directory of the scaffolding wasn't updated for using runResourceT in
database accesses.  As well as correcting this, I have added a trivial example test
case to HomeTest.hs, both as a self-test of the fix and to help users get started.
I have chosen to re-export the required things via TestImport.

This *postgres* version applies to the other SQL database branches too, of course - I'll
do another pull request for the *mongo* branch, and **none** of this goes into *simple*.

If you would prefer separate pull requests for all the branches, give me a shout - I've
already built and tested them using the tools provided, and pushed them to my fork.
I don't know whether you want to maintain the merging between branches, so I've
tried to err on the simple side for now.