TODO:
* support multiple data ranges in plot (T13016)
* support 1/x axis scale
* SpreadsheetView: implement getBigInt() using QLineEdit with QLongLongValidator inherit from QValidator (see https://stackoverflow.com/questions/19865535/qt-qinputdialog-how-to-validate)
* implement the interruption of running calculations in Maxima, borrow the code from wxMaxima for this
* Expose 2D-structure in CAS as Matrix and allow to plot the columns of it
DONE:
* add KUserFeedback on Windows and Mac (Stefan)
Links:
* TODO list: T11524
* Windows port: T3118, T11868, T11669
* Mac port: T3196