Bugs causing it to not be able to un-zoom.

I don't think it's needed anywhere in QGC since this has been a bug for a long time.

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

This crash could be reproduced by starting QGroundControl, switching to
plot, then clicking the "Symmetric" checkbox.

Further consolidation of Plot code into ChartPlot. Also removed some unused variables from LinechartWidget.cc. Also only active curves are recolored in the IncrementalPlot class.

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.

Working on QGraphicsView-based local waypoints interface supporting drag-and-drop, commented code, fixed Google Maps interface, added mouse and SpinBox zoom to HSIWidget, fixed MAV-based coloring and stylesheets - MEGA COMMIT

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