Update includes to to be relative to src directory

Don't use relative imports like `../foo.h` as those depend on the
relative position of both files. Rather than that use imports relative
to the `src` directory, which explicitly is part of the include
directories.

src/displayapp/DisplayApp.h

@@ -5,9 +5,9 @@
 #include <task.h>
 #include <memory>
 #include <systemtask/Messages.h>
-#include "Apps.h"
-#include "LittleVgl.h"
-#include "TouchEvents.h"
+#include "displayapp/Apps.h"
+#include "displayapp/LittleVgl.h"
+#include "displayapp/TouchEvents.h"
 #include "components/brightness/BrightnessController.h"
 #include "components/motor/MotorController.h"
 #include "components/firmwarevalidator/FirmwareValidator.h"
@@ -17,7 +17,7 @@
 #include "components/alarm/AlarmController.h"
 #include "touchhandler/TouchHandler.h"
 
-#include "Messages.h"
+#include "displayapp/Messages.h"
 #include "BootErrors.h"
 
 namespace Pinetime {