Removing TreeModel specific HTML printer for CM.

TreeModel now uses CM#toHTML method to print CM instead
of its own code.
Variable importance for DRF regression trees.

Measured as permutation importance of MSE.
Small fix in varimp computation for regression trees.
Disable static height of varimp graph.

Now graph is scaled by number of variables. Each variable
bar has a static height.
Merge branch 'master' of github.com:0xdata/h2o
Merge branch 'master' of github.com:0xdata/h2o into REG
Skip decided nodes with impossible splits.
Merge branch 'master' of github.com:0xdata/h2o into REG
Minor UI fix.

Increased size of bar.
Merge branch 'master' of github.com:0xdata/h2o into REG
More improvements for GBM variable importance.

UI now reports
 - raw scores as reported by R call relative_influence(model)
 - scaled scores as reported by R call: relative_influence(model, scale=T)
   - scaled with respect to maximum score
 - summary of scores reported in % with respect to a sum of scores
   - R call: summary.gbm(model)
Merge branch 'master' of github.com:0xdata/h2o into REG