FIX: use next(iterator) built-in instead of iterator.next()
MAINT zap unused import
DOC optimized PNG images with OptiPNG

Did "optipng -o 10" on all the files with OptiPNG 0.6.4.
This shaves a total of 529012 bytes off the pictures.
DOC remove qda and faces from website carousel

... in order to speed up the website, as discussed at #2477.
DOC replace jquery by minified version

Still 1.7.2, as I saw in the history that @jaquesgrobler had
previously downgraded to this version.
Merge pull request #2479 from larsmans/website-speed

[MRG] improve website speed, hopefully
FIX : cleanup coef_init in coordinate descent
GBRT enhancements:
  Moved verbose output code to VerboseReporter class.
  Cosmit: logical structured code blocks
  Refactored: moved init state to method
  Added partial_fit to GradientBoosting
  Fix: is_classification not available; n_features not n_features_
  Tests
  Add ``partial_fit`` to docs
added EPSILON_FLT and EPSILON_DBL for almost equal impurity and fx value comparisons
fiddled with EPSILON_DBL
added monitor callback w/ early stopping support
fix: VerboseReporter remaining time in the case of partial_fit