Add *-devel output to conda-forge packages that require them #133

A common failure point in robostack is that we have conda-forge C++ libraries packages that do not have an output that can be installed to ensure that all the dependencies required to build a downstream C++ project. This is not an issue if a C++ package already include its headers and only use as public dependencies in its headers conda-forge libraries that also ship their headers in the main package, but as soon a dependency uses in its headers a dependency that ships its headers in a separate *-devel package, we need to have a *-devel output also for that package, or it needs to adds the *-devel package to its run dependencies, but some mantainer may be against this as it goes around the point of splitting *-devel packages.

Problematic packages:

• qt-main : Depends on libgl-devel, but at runtime it only requires libgl
• vtk : Depends on qt-main, i.e. inheriting the libgl-devel problem
• pcl: Depends on qt-main, i.e. inheriting the libgl-devel problem
• libspnav : Depends on xorg-xorgproto, as @Tobias-Fischer is the maintainer and the package is quite simple probably we can avoid the libspnav-devel output and just add xorg-xorgproto as run dependency.