Committing this separately from the rest to ease making a patch for just this
  functionality in case that it might make it into the trunk.
  
  This can function standalone, though it is less useful without the rest.
  It requires that wxwidgets-3.0.0_macosx_magnify_event.patch be applied to wxWidgets
  It is completely optional; everything is guarded by the USE_OSX_MAGNIFY_EVENT macro.
  
  - Added OnMagnify event handler to EDA_DRAW_PANEL, EDA_3D_CANVAS and the helper for
    EDA_DRAW_PANEL_GAL, WX_VIEW_CONTROLS. This should cover canvases all current tools.
  - Guarded all with USE_OSX_MAGNIFY EVENT feature macro and added support in CMakeLists.txt