Improvements

[MatthijsBurgh]

• [rgbd] Add rate to loop
• [rgbd] include cv::Mat header
• [rgbd] add opencv dep in package.xml
• [rgbd] find_package opencv in CMakeLists.txt
• [rgbd] improve dep levels in package.xml
• [main] add opencv dep in package.xml
• [main] find_package opencv in CMakeLists.txt
• [main] improve dep levels in package.xml