Added all *.cpp samples reference to the documentation

Added a link in documentation pointing to samples containing the functionality.
Did it only for the samples that have functionality in the 2.4 branch.

Suggestion was made in this feature request:
http://code.opencv.org/issues/3169 

If this works out and gets merged, will consider doing same for other sample folders also.
Also want to know if it is usefull to add C samples, since we want to demotivate people using the interface?