* GSoC 2016 - Adding toggle files to be used by tutorials.

Add a toggle option for tutorials.
* adds a button on the HTML tutorial pages to switch between blocks
* the default option is for languages: one can write a block
for C++ and another one for Python without re-writing the tutorial

Add aliases to the doxyfile.
* adding alises to make a link to previous and next tutorial.
* adding alias to specify the toggle options in the tutorials index.
* adding alias to add a youtube video directly from link.

Add a sample tutorial (mat_mask_opertaions) using the developed aliases:
* youtube alias
* previous and next tutorial alias
* buttons
* languages info for tutorial table of content
* code referances with snippets (and associated sample code files)

* Removing the automatic ordering.
Adding specific toggles for cpp, java and python.
Move all the code to the footer / header and Doxyfile.
Updating documentation.

Documentation fixes for latest doxygen

This is based on testing OpenCV 3.1 with VisionWorks, which identified issues.
The tutorial now specifies 3 cherry-pick commands for opencv.

Some function calls to Media Foundation can fail and retrun null
pointers. They should be checked before being dereferenced to avoid a
crash.

Update linux_install.markdown

Update linux_install.markdown

Update linux_install.markdown

Update linux_install.markdown

Update linux_install.markdown

Update linux_install.markdown