wave_matching const correctness

[leokoppel]

Currently using wave_matching it is very hard to write a const-correct program. The library itself should be const correct.

It may also be preferable to accept references to PointCloud instead of references to smart pointers, but probably best to be consistent with PCL. Note the difference between const shared_ptr<T> and shared_ptr<const T>.

Current

Functions accept PointCloud::Ptr arguments even though they never change the input

Desired

• Functions should accept accept const PointCloud& arguments when they never change the input.
• Functions should accept PointCloud::ConstPtr& arguments if they need to modify the smart pointer itself.
• Maybe const PointCloud::ConstPtr & is OK because PCL interface is written this way.