Do not print giant Java models by default

Big Tree models (e.g. 50 trees x 2 classes x 10000 leaves per tree) make
for Big Java - which we were printing to the browser with each
progress-bar update.
Move SB to its own file, so others can use it.
Peel out the Java generation from the API, into its own methods.
Merge branch 'master' of github.com:0xdata/h2o
Merge branch 'master' of github.com:0xdata/h2o