Modify tutorials to point to the new data sources

Modifications as per [this thread](http://www.pcl-developers.org/PCD-data-repositories-td5708156.html).

    find . -name "*.rst" -exec sed -i 's|http://svn.pointclouds.org/data|https://raw.github.com/PointCloudLibrary/data/master|g' {} \;