- use per-module includes instead of "opencv.hpp"
- unused function warnings
- undefined macro warning

Fix bug in camera_calibration.cpp that the program tries to
parse input of type VIDEO_FILE as IMAGE_LIST which causes the
program to crash.

    * correct the part about fixed aspect
    * improve formatting
    * add snippet markers to source
    * replace inline code by @snippet
  - do not run calibration twice when using a imageList
  - make output consistent in itself (CamelCase vs no_camel_case) as well as with old camera calibrate sample
  - respect write extrinsic/ points flags
  - set the aspectRatio value when specified
  - fix writing of calibration settings. also update grammar.
  - fix intendation and remove some size_t -> int casts by using size_t

Also fixed some typos and code alignment
Also adapted tutorial CPP samples
Fixed some identation problems

These codes should be included into regular builds.

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.