LIBTD-1405: SEAMUS Import Cleanup

After running the rake tasks to import SEAMUS data (#10 ), run the following cleanup task:

bin/rake seamus:cleanup_works

This script will downcase emails and prune empty descriptions, scores, and durations from the recently imported SEAMUS data.

[Edit: Now, all SEAMUS users should have at least one associated work.]

I realize I left out the downcase of the contributor/performer email when I tried to rework the code. I just added it back in. Sorry for the additional change!