Copy generated tutorials to Git repository folder (instead of moving)

With `mv` the following error occurs:

mv: cannot move `/home/travis/build/PointCloudLibrary/pcl/build/doc/tutorials/html' to `/home/travis/build/PointCloudLibrary/pcl/build/doc/doxygen/html/tutorials/html': Directory not empty
Merge pull request #779 from taketwo/travis-cp-instead-of-mv

Copy generated tutorials to Git repository folder (instead of moving)
Set compute3Dcentroid last component to 1
Merge pull request #781 from VictorLamoine/master

Set compute3Dcentroid last component to 1
Updated PCL compilation instructions with details about compiling and
using tests. Addresses #784, with thanks to @taketwo.
Merge pull request #786 from mohawkjohn/make_tests_doc_update

Updated PCL compilation instructions for contributors wanting to run `make tests`