cnn_3dobj: fix include and allow compilation of samples

[paroj]

caffe/vision_layers.hpp is gone. also fix some warnings.

fixes #580

[sovrasov]

@paroj please use resolves instead of fixes in the first comment (in this case the corresponding issue will be closed by buildbot when PR will be merged) and use WIP keyword if you are planning to add more commits into the PR.

[alalek]

resolves instead of fixes

Actually both are valid for GitHub: https://help.github.com/articles/closing-issues-via-commit-messages.
But please don't use this functionality in commits directly (PR description is the optimal way).

**WIP** in description doesn't run automatically any builds (this may be a problem because there is no access to rerun any builds). After remowing WIP you need to push new commits (or to amend previous commint and force push) to run automatic builds again.

[paroj]

@sovrasov this is not WIP. I just tend to add commits on existing PRs instead of opening new ones.

[sovrasov]

I have an error here:
could not read reference image /home/user/repositories/opencv_extra/testdata/cv/4_78.png

[paroj]

currently, you still have to set
export OPENCV_TEST_DATA_PATH=<opencv_contrib>/modules/cnn_3dobj/testdata

see: https://github.com/opencv/opencv_contrib/tree/master/modules/cnn_3dobj

[sovrasov]

Ok, lets wait for opencv/opencv#7750. It allows to add different testdata sources using ocv_add_testdata macro in CMake.

[paroj]

done

[alalek]

@paroj Please apply these changes.
After that you can put OPENCV_TEST_DATA_PATH back to <opencv_extra>/testdata

[alalek]

Thank you! 👍

[mshabunin]

@paroj , can you please confirm whether we need changes from #453