Multi face support, analog clock, 12/24 config

src/displayapp/screens/Screen.h

@@ -7,6 +7,26 @@ namespace Pinetime {
   namespace Applications {
     class DisplayApp;
     namespace Screens {
+
+      template <class T>
+      class DirtyValue {
+        public:
+          DirtyValue() = default;                      // Use NSDMI
+          explicit DirtyValue(T const& v):value{v}{}   // Use MIL and const-lvalue-ref
+          bool IsUpdated() const { return isUpdated; }
+          T const& Get() { this->isUpdated = false; return value; }  // never expose a non-const lvalue-ref
+          DirtyValue& operator=(const T& other) {
+            if (this->value != other) {
+              this->value = other;
+              this->isUpdated = true;
+            }
+            return *this;
+          }
+        private:
+          T value{};            // NSDMI - default initialise type
+          bool isUpdated{true}; // NSDMI - use brace initilisation
+      };
+      
       class Screen {
         public:
           explicit Screen(DisplayApp* app) : app{app} {}