Added missing word and link

Based on the keypoints found we have to +extract+ features (linked tutorial which explains how features work in pcl)
Add an overload of pcl::io::savePNGFile().

The new function takes sensor_msgs::Image and saves it as a PNG file.
Currently supported are "rgb8", "mono8", and "mono16" image encodings.
Add PointCloudImageExtractor base class and several implementations.

* PointCloudImageExtractorFromRGBField produced a color image based on
  the data in "rgb" field of a point cloud.
* PointCloudImageExtractorFromNormalField produced a color image based on
  the data in "normal" field of a point cloud.
* PointCloudImageExtractorFromLabelField produced a mono image based on
  the data in "label" field of a point cloud.
* PointCloudImageExtractorFromZField produces a mono image based on the
  "z" field of a point cloud.
* PointCloudImageExtractorFromCurvatureField produces a mono image based on the
  "curvature" field of a point cloud.
* PointCloudImageExtractorFromIntensityField produces a mono image based on the
  "intensity" field of a point cloud.
Add an overload of pcl::io::savePNGFile().

The new function takes a field name and uses appropriate
PointCloudImageExtractor subclass to extract an image from the given
field. Currently supported are "normal", rgb", "label", "z",
"curvature", and "intensity" fields.
Add pcd2png application to the "tools" module.
Add tests for Point Cloud Image Extractors.
fixed recognition cmake file and added ransac_based recognition headers at old locations which include the headers at the new locations and deprecation warnings.
CMake changes were not included in previous commit.  Now they are
recognition/CMakeLists.txt now installs the old header files along side the new ones.  Only the new header files were installed in the previous commit
Modify tutorials to point to the new data sources.
uncommented old implementation files includes in recognition/CMakeLists.txt
ransac_based/ was missing from path to old headers causing error in cmake.  Fixed it.
update covariances only if a new pointcloud was set

this avoids unnecessary recalculations if only one of the pointclouds has been changed
Added missing PCL_EXPORTS macro to pcl::on_nurbs::FittingCylinder to allow linking.
Added nurbs cylinder fit with defined axes - first one is used as cylinder axis
Added function declaration for initNurbsCylinderWithAxes
Fix for issue #284 - just needed eigen align macro
Fix: only left button press event was invoked
Add: ability for user to set its own interactor style
Fix: addRectangle as of VTK 5.8 handling y coordinates