Test alphamatte

[muskaankularia]

Merge with extra: opencv/opencv_extra#668

When this pull request gets merged
resolves #2245

This pull request changes

added CMakeLists.txt to #2245.

opencv_extra=master

[muskaankularia]

@alalek I am getting errors/warnings in my doc, can you please take a look at it and help me in resolving the issues?
I am getting this following warning -
/build/precommit-contrib_docs/opencv_contrib/modules/alphamat/tutorials/table_of_content_alphamat.markdown:4: warning: unable to resolve reference to tutorial_information_flow_matting' for \ref command /build/precommit-contrib_docs/build/doc/root.markdown:31: warning: unable to resolve reference to alphamat' for \ref command

I think it's not able to find the file(tutorial_information_flow_matting) but its already there.

Thanks

[asmorkalov]

General comments on PR:

• Please remove dead code from sources
• It's bad idea to place images in module source code directory. Please move it samples directory or tests directory, if they are really needed
• Please use OpenCV data structures and not expose 3rd party library structures as interface. Let's discuss details, if it's not possible or very ineffective.
• GTest and OpenCV test can handle disabled tests, please add DISABLED_ prefix to commented tests. They'll be reported as disabled during test run.

[asmorkalov]

Doxygen reports warnings:

/build/precommit-contrib_docs/opencv_contrib/modules/alphamat/tutorials/table_of_content_alphamat.markdown:4: warning: unable to resolve reference to `tutorial_information_flow_matting' for \ref command
/build/precommit-contrib_docs/build/doc/root.markdown:31: warning: unable to resolve reference to `alphamat' for \ref command

[alalek]

Please keep all project work in a single PR: #2245

[sunitanyk]

Hi @asmorkalov,

The GSoC intern who initiated this PR and PR#2245 is not available time-wise now(as she has another full-time job) to be able to finish this PR soon. I am the mentor of the project and can help in merging it into contrib. I will need to create a new PR with your changes in that case, right?