Pushed new branch T22819-generalizeC3jsAPI.

Already had a first look. While it works and it is indeed more general as the first version, I'm not very happy with the interface/design of the classes. It's quite hard to understand, internal stuff is exposed, and it has a monolithic character. But no worries, I'll come up with something more constructive soon. :D

Got feedback from @kislinsk to change a bit the public functions and do polish.
Create a new integration-branch from master as quite some changes were done meanwhile.

feedback from @kirchnth branch doesn't build on Ubuntu

smartpointer conversion errors e.g.

[...]/Plugins/org.mitk.gui.qt.measurementtoolbox/src/internal/QmitkImageStatisticsView.cpp:185:56: error: conversion from 'itk::Statistics::Histogram<double>::Pointer {aka itk::SmartPointer<itk::Statistics::Histogram<double> >}' to non-scalar type 'itk::Statistics::Histogram<double>::ConstPointer {aka itk::SmartPointer<const itk::Statistics::Histogram<double> >}' requested
         this->m_CalculationThread->GetTimeStepHistogram(timestep);

Pushed new branch T22819-mitkChartIntegration.

Pushed new branch T22819-ubuntuWarningFixes.

fixed some gcc warnings as errors - i still cant actually see a chart under ubuntu

I will investigate the Ubuntu problems

Chart works on my virtual machine (Ubuntu 16.04 with Qt 5.7)
@kirchnth tries again with Qt 5.7.