clear display on init to avoid static

src/helpers/ui/DisplayDriver.h

@@ -15,6 +15,7 @@ public:
   virtual bool isOn() = 0;
   virtual void turnOn() = 0;
   virtual void turnOff() = 0;
+  virtual void clear() = 0;
   virtual void startFrame(Color bkg = DARK) = 0;
   virtual void setTextSize(int sz) = 0;
   virtual void setColor(Color c) = 0;

src/helpers/ui/SSD1306Display.cpp

@@ -20,6 +20,11 @@ void SSD1306Display::turnOff() {
   _isOn = false;
 }
 
+void SSD1306Display::clear() {
+  display.clearDisplay();
+  display.display();
+}
+
 void SSD1306Display::startFrame(Color bkg) {
   display.clearDisplay();  // TODO: apply 'bkg'
   _color = SSD1306_WHITE;

src/helpers/ui/SSD1306Display.h

@@ -27,6 +27,7 @@ public:
   bool isOn() override { return _isOn; }
   void turnOn() override;
   void turnOff() override;
+  void clear() override;
   void startFrame(Color bkg = DARK) override;
   void setTextSize(int sz) override;
   void setColor(Color c) override;