Add CSV output reporting.

It's too late and I'm not entirely happy with `CSVReporter` and especially `CSVReporterTest` but the CSV feature is too cool to wait. Would appreciate improvements.

Pretty much passed on `PluginTest.groovy` entirely. This needs tackling separately.

Can't wait to get these CSV data files into R and start making some plots!
You can use `.toBoolean()` here. It has some arcane magic in it making `"0"` and `"false"` evaluate to false whereas `"1"` and `"    trUE"` evaluate to true.