Upgrade libraries

Thought it might be quick to take out all the v1 stuff from the Scala client (hence the branch name). Turns out that's not the case, but whilst investigating I ended up moving to `build.scala` and upgrading the libraries. (Though we will still need to do the v1 feature exorcism.)

I've set the next version to be released as 3.0.

:raising_hand: :train: