Random wartremover and lint cleanups

Lots of minor tweaks based on -Xlint and enabling wartremover.

I would like to switch -Xlint on permently but it falls over on some of the akka code (inference of any).
I'll add comments on the various changes so you can see what they are based on.
The modern convention is ```foo():Unit = {}``` rather than pure method sytax ```foo() {}```