Add Stopwatch application

It can be started, stopped, and cleared. It also continues to run if
you leave the screen.

firmware/Application/Screens/StopwatchScreen.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2019  Max Regan
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#pragma once
+
+#include "Application/ScreenManager.h"
+#include "Bsp/Drivers/DisplayDriver.h"
+#include "Bsp/ReturnCode.h"
+#include "Bsp/Task.h"
+#include "Bsp/Time.h"
+
+class StopwatchScreen : public Screen {
+public:
+
+    StopwatchScreen(BSP::DisplayDriver &display,
+                    ScreenManager &m_manager);
+
+    BSP::ReturnCode init();
+    BSP::Schedule::NextTime execute() override;
+
+    void enable() override;
+    void disable() override;
+    void notify_up_button() override;
+    void notify_middle_button() override;
+    void notify_down_button() override;
+
+private:
+
+    void display_number(uint32_t *x, uint32_t y, uint32_t tens, uint32_t ones);
+    void display_number(uint32_t *x, uint32_t y, uint32_t hundreds, uint32_t tens, uint32_t ones);
+    void refresh();
+    void add_time();
+
+    BSP::DisplayDriver &m_display;
+    ScreenManager &m_manager;
+
+    bool m_is_running;
+    BSP::time_t m_accumulated_time;
+    BSP::time_t m_last_time;
+    const struct font &m_font;
+};