enhancement requrests

[omerbrandis]

hello ,

( noticed some other "issues" with building this repo with other lib versions ,
also considering that both pcl 1.8.0 and vtk 8.1 are not available any more ,
i've manged to build in a docker container based on nvidia/opengl:1.2-glvnd-devel-ubuntu18.04
then installed vtk 8.2, pcl 1.9.1 ).

anyway,
I've manged to run the app, and display my pcl,
but, navigation is a bit uncomfortable.
would it please be possible to :

1. add the ability to rotate the pcl on each axis individually ?
   ( rotating with the mouse was not natural to me, and very quickly lead to situations where the displayed axes where not inline with the world axes)
2. allow switching between coordinate systems ,
   i mean , i would positive x to be to the right ( when positive z is forward )
   ( its the other way around right now )

thanks,
Omer.