remove unused applet-related code
minor cleanup in api.ModelReader
use .toVector now that we're on Scala 2.10
enable scalac -Xlint in extension builds
tweaks as needed to pass scalac -Xlint

a lot of this was about sorting out confusion about nullary methods
in Scala and overriding them in Java, since Java doesn't have nullary
methods.  I converted more of AbstractWorkspace to Scala to sidestep
the problems.  see e.g. SI-6978
enable scalac -Xlint in headless project

it would be nice to someday enable it for the main project too