Fix major build.sh mystery

build.sh was rebuilding all class files in lib/water when compiling
just the initializer part... so stop that.  No more javac when building
the initializer, just copy the already build class files into lib when
cooking up the one-jar.  This also means no more top-level lib/water
classes, so the SampleMain cannot link against water.* so change all
the external interfaces to use plain Object.