Add favicons.

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Add NLopt and CMA-ES plugins to the Travis-enabled packages.
Add result of optimization in Getting started section.
Fix objective function in getting started.
Move PaGMO to experimental solvers.
Add includes in getting-started to help new users.
Add showcase (papers only for now).

Implement #3.
Add more papers.
Add even more papers.
Add Google verification file.
_layouts/default.html: add Google Analytics
Add preliminary results for benchmarks.
benchmark.html: prettify solver names in chart
benchmark.html: add horizontal axis to chart
benchmark.html: fix typo :lipstick:
benchmark.html: sort data over x-axis
benchmark.html: remove failed tests by hand (for now)
benchmark.html: add methodology, enhance graph rendering
benchmark.html: aesthetic changes :lipstick:
benchmark.html: explain why some problems have alternative implementations