Transform point cloud in GICP align function

Fixes #754 and #818 
I also fixed a dead link in the GICP documentation.

The new changes can be tested using the following code; which is a modified copy of [Interactive ICP](http://pointclouds.org/documentation/tutorials/interactive_icp.php) tutorial code. [Test project](https://gist.github.com/VictorLamoine/20ef23dcb7cf6ef93cdd)

I use a GICP object rather than an ICP object; here I use the `align` function with a guessed matrix 
`icp.align (*cloud_icp, transformation_matrix.inverse ().cast<float> ());`

Note that `transformation_matrix.inverse ()` is the exact transformation to align the point cloud. As a result the point cloud is perfeclty aligned after the first iteration.

If you want to see GICP working just use
`icp.align (*cloud_icp);`
And press space in the viewer to iterate!