Using QFileDialog directly on OS X can hang intermittently due to Qt
bug.

I was unsure how to update the QwtPlotPrintFilter code, so I just commented it out with a FIXME.

Moved all shared code for IncrementalPlot and LinechartPlot into a common ChartPlot superclass. Also recoloring the background of both widgets now works when switching between color schemes.

Also changed calculateRegression(...) to return a bool, as that's all it needs.

Fixed a stack overflow bug when using the regression fitting command in logfile plot. Solution involved just allocating on the heap instead of the stack.

Significantly improved plotting, now capturing data in linechart allows limmediate processing / analysis of the whole flight