Merge pull request #1771 from tklein23/csgobject_refactoring

CSGObject refactoring: Introduced SGRefObject
update news
- add dynamic array for SGRefObject's
- make SGRefObject the class that is swig ref/unref'd
fix typo and documentation of SGRefObject
Fixing wrong class names in SGDynamicRefObjectArray.
StructuredLabels now uses DynamicRefObjectArray (holding SGRefObjects) instead of DynamicRefObjectArray (holding CSGObjects)
Class CStructuredData does now extend SGRefObject instead of CSGObject
* Renamed CStructuredData to StructuredData.
* Need to removed the "C" in CFactorGraphObservation, CSequence and CRealNumber, because they
  do not know how to serialize.
* Fixed unit tests/examples to reflect new names.
* Added basic test for RealNumber labels.

Conflicts:
	src/shogun/labels/StructuredLabels.cpp
Updated class names in SWIG mapping.
Finally, to avoid overhead for StructuredData, the container class StructuredLabels
now uses thin SGDynamicRefObjectArray instead of fully-featured CDynamicRefObjectArray.