Warning cleanup, fix travis config

src/visual/ImagePanel.cpp

@@ -10,7 +10,7 @@ ImagePanel::ImagePanel(wxPanel * parent, wxString file, wxBitmapType format) :
 	image.LoadFile(file, format);
 }
 
-void ImagePanel::paintEvent(wxPaintEvent & evt) {
+void ImagePanel::paintEvent(wxPaintEvent & /* evt */) {
     wxPaintDC dc(this);
     render(dc);
 }

src/visual/TuningCanvas.cpp

@@ -250,7 +250,7 @@ void TuningCanvas::StepTuner(ActiveState state, int exponent, bool up) {
     }
 }
 
-void TuningCanvas::OnIdle(wxIdleEvent &event) {
+void TuningCanvas::OnIdle(wxIdleEvent & /* event */) {
     if (mouseTracker.mouseDown()) {
         if (downState != TUNING_HOVER_NONE) {
             dragAccum += 5.0*mouseTracker.getOriginDeltaMouseX();

src/visual/WaterfallCanvas.cpp

@@ -483,7 +483,7 @@ void WaterfallCanvas::OnKeyDown(wxKeyEvent& event) {
     }
 
 }
-void WaterfallCanvas::OnIdle(wxIdleEvent &event) {
+void WaterfallCanvas::OnIdle(wxIdleEvent & /* event */) {
     processInputQueue();
     Refresh();
 }