svm/OnlineLibLinear: Added learning of StreamingSparseFeatures:
* Added method "train_one" for sparse vectors (a lot code duplication!  sorry!)
* "train_example" now consumes CStreamingDenseFeatures and CStreamingSparseFeatures
* Added bounds checking in CStreamingSparseFeatures<T>::dense_dot
  (allowing sparse dot-product with shorter weight vector)

Refactoring in StreamingSparseFeatures
* removed duplicate "expand_if_required" - already implemented in features
* avoided manual resizing of vectors using low-level stuff like realloc/memset/etc.
svm/OnlineLibLinear: Added learning of StreamingSparseFeatures:
* Added method "train_one" for sparse vectors (a lot code duplication!  sorry!)
* "train_example" now consumes CStreamingDenseFeatures and CStreamingSparseFeatures
* Added bounds checking in CStreamingSparseFeatures<T>::dense_dot
  (allowing sparse dot-product with shorter weight vector)

Refactoring in StreamingSparseFeatures
* removed duplicate "expand_if_required" - already implemented in features
* avoided manual resizing of vectors using low-level stuff like realloc/memset/etc.
Added example for OnlineLibLinear with streaming sparse features.
* Renamed examples more consistently.
* Enabled new example in CMakeLists.txt
Minor spelling and formatting changes accoring to review.
Used `$ git config -f .gitmodules submodule.data.branch master`: Making submodule
`data` track branch `shogun-data/master` automatically.
added part about FITC large scale regression since roman fixed the bugs recently
initial draft for (x-) evaluation, and model selection notebook
Merge pull request #1790 from tklein23/develop

Submodule `data` tracks branch `shogun-data/master`automatically.
Merge pull request #1785 from tklein23/example_classifier_onlineliblinear_sparse

Added example for OnlineLibLinear with streaming sparse features.
Merge pull request #1783 from tklein23/online_learning_sparse_stream

svm/OnlineLibLinear: Added learning of StreamingSparseFeatures
add shogun namespace to ref/unref
do not call exit_shogun in java / csharp examples

- calling exit_shogun at the end of a java / csharp example is
dangerous: not all shogun objects might have been freed by the garbage
collector at this stage so calling exit_shogun was observed to destroy
essential helper objects that all shogun objects require at runtime
leading to unexpected crashes.
test cross validation fold indices
modified one file to include all tests
remove file
fixed typos in crossvalidation tests
Merge pull request #1796 from karlnapf/develop

added FITC part of GP notebook and X-validation notebook draft
test covering of all indices
test covering of all indices