Merge pull request #2165 from kislayabhi/develop

added PCA notebook to the NEWS.
memory leak fixed
Merge pull request #2166 from mazumdarparijat/decision_tree

memory leak fixed
add to news
Merge pull request #2168 from Saurabh7/develop

minor changes mkl nb
Added factor graph model for multilabel classification example in libshogun.
Merge pull request #2032 from Jiaolong/fg_multilabel_cvc

Entrance task #1916: factor graph model for multi-label classification example - thanks to Jiaolong
fixed errors in ID3ClassifierTree unittest
Merge pull request #2172 from mazumdarparijat/decision_tree

error in ID3ClassifierTree unittest fixed
fixed legends and plots in PCA notebook.