LabPlot builds and runs with kf5

[Alexander Semke]

Hi Marco, Hi Scarlett,

> just for your information, Scarlett’s new multi-platform CI system already
> allows - apart from the obligatory Linux - for building on OSX. :-)
that's really great. Thank you for this!

> Although playground or review projects are usually not in CI I introduced
> you project, so that you’ll have better insight into where things fail:
We'll move to extragear soon, I hope :-)  

> https://build-sandbox.kde.org/view/FAILED%20OSX%20(KF5)/job/labplot%20frame
> works%20kf5-qt5/
> 
> This might help you figuring out a solution on your own, without me testing
> patches for you...
> 
> PLUS you don’t need your own OSX setup for all of this.
I still would like to setup the dev-environment on my old macbook to fix 
problems like this. So, if there is somewhere a brief documentation for how to 
setup kf5 on OSX, please tell me :-) The CI-job on the jenkins server will 
help to observe and to keep the mac os build stable without the need to 
compile the project every time on OSX locally.

Regards
Alexander