(2.4) Backports from master branch (#7854)

* expose 2 extra methods from ml::TrainData: getNames() and getVarSymbolFlags(). The first one returns text labels from CSV (if the data has been loaded from CSV); the second one returns a matrix of boolean values; its n-th element is 1 iff the corresponding column in the CSV uses symbolic names, not numbers.

* check that the dynamic_cast succeeds

Added some asserts.

Added function makeData() in test_svmsgd.cpp.

Also fixed documentation, refactored sample.

related to issue 4969
fixes issue 5891
fixes issue 5922

Someone forgot to wrap the load function for SVMs in the
corresponding ml python module. Fixed that.

Update docs according to PR #5127

misplaced CV_WRAP statement lead to not exposing EM::getCovs() to python/java/matlab wrappers

add a CV_OUT to return the covs properly

2. Algorithm::load/save added (moved from StatModel)
3. copyrights updated; added copyright/licensing info for ffmpeg
4. some warnings from Xcode 6.x are fixed

REG_NONE defined in ml.hpp conflicts with defined in Winnt.h

- fixed one BiB record
- moved algorithms overview to separate page
- added docs for some enumerations
- fixed some small documentation errors