Cleanup sbt keys

Make it `optimizerMode` then. I repeat: the optimizer does many more things besides inlining. It simply does not make sense to talk about an "inliner" at all. We've got an "optimizer". It so happens that this optimizer does inlining, but it also does constant folding, scalar replacement, closure elimination, etc. Basically we should *never* write "inliner" or "inlining" *anywhere* (except within `OptimizerCore.scala`, of course). We should write "optimizer" instead.