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
DOC typo: polynominial
FIX : warm_start in coordinate_descent (was ignored)
FIX : set deprecation to 0.16 in coordinate descent
API : set return_models to False by default in path functions in coordinate descent
FIX Pipeline should raise ValueError for duplicate name

It previously raised a TypeError because the construction of the
exception was done wrong. Fixes #2471.
MAINT list @paulgb's full name
FIX : get rid of convergence warning in test_coordinate_descent
ENH : Gaussian process for arbitrary-dimensional output spaces by @JohntheBear
ENH : simplify input checking in GP
update what's new
DOC improve biclustering docstrings

I had to figure out by experimentation what the methods were doing.
ENH sparse matrix support in pairwise + optimizations
ENH optimize NMF inner loop

The call to np.maximum was taking 20% of the time.
Multiplying by Hn > 0 is about twice as fast.

This reverts commit 6ef08cfac27cda790a5d0d2dd2da82bf744905eb.
FIX max_features in CountVectorizer

Fixes #2443: max_features would be selected based on document frequency
rather than term frequency.
COSMIT pyflakes feature_extraction.text tests