Allow building wave_matching without visualization

[leokoppel]

Platform

Platforms without pcl_visualization, perhaps without displays at all

Observed result

Build fails with libwave/wave_matching/include/wave/matching/pointcloud_display.hpp:23:46: fatal error: pcl/visualization/pcl_visualizer.h: No such file or directory

Desired result

wave_matching builds and is usable, except for visualization features

There are some decisions to be made. For example

• Does wave_matching build in different configurations via preprocessor directives, or is there a separate module, e.g. wave_matching_visualization, which depends on pcl_visualization?
• If the former, is the PointCloudDisplay class simply not built, or is it built as an empty interface with all its methods doing nothing (perhaps printing a warning at compile time)? That would allow client code to be compiled without changes for headless platforms, but is more complicated.