Upgrade code to support OpenCV 3 on ROS Melodic

[abougouffa]

Some modifications to viodom to be compiled with OpenCV 3 on ROS Melodic.

[fjperezgrau]

Thanks a lot for your contribution @abougouffa. I have created a branch called opencv3 so please could you do the pull request on that branch instead of the master branch?

[abougouffa]

You are welcome, thank you for sharing your code @fjperezgrau
It is done 😃

[fjperezgrau]

Thanks again. After reviewing the commits, I realized that the vast majority of changes are caused by format settings. In order to keep the same style, since other colleagues are using this, I'd kindly ask you to submit the minimal changes needed to compile and use the package with OpenCV3 and ROS melodic, i.e. changes in CMakelists.txt and src/robustmatcher.hpp are fine, but changes in src/stereodom.hpp are far more than the necessary ones for using the new features.