e.g. <opencv2/core/core.hpp> become <opencv2/core.hpp>

Also renamed <opencv2/core/opengl_interop.hpp> to <opencv2/core/opengl.hpp>

updated links in cheatsheet
renamed directory for Mat tutorial 
changed links from willow docs to opencv.itseez.com, from Trac to current Redmine

Added the "Camera calibration With OpenCV" tutorial. Extended with a few global links the conf.py file. Corrected an error in the linux_install.rst and one in the cascade_classifier.rst file.