Merge pull request #821 from fdlamotte/ui_gps_page

ui_task: initial gps page

src/helpers/sensors/EnvironmentSensorManager.h

@@ -39,6 +39,7 @@ protected:
 public:
   #if ENV_INCLUDE_GPS
   EnvironmentSensorManager(LocationProvider &location): _location(&location){};
+  LocationProvider* getLocationProvider() { return _location; }
   #else
   EnvironmentSensorManager(){};
   #endif

src/helpers/sensors/LocationProvider.h

@@ -17,8 +17,8 @@ public:
     virtual bool isValid() = 0;
     virtual long getTimestamp() = 0;
     virtual void sendSentence(const char * sentence);
-    virtual void reset();
-    virtual void begin();
-    virtual void stop();
-    virtual void loop();
+    virtual void reset() = 0;
+    virtual void begin() = 0;
+    virtual void stop() = 0;
+    virtual void loop() = 0;
 };