Refactoring, housekeeping, documentation

Add a class diagram. Still needs some details.
Refactor to better respect SOLID principles.
Housekeeping, move and rename classes/files.

app/src/sensor/GPUSensorsFacade.cxx

@@ -0,0 +1,9 @@
+#include <sensor/GPUSensorsFacade.h>
+
+#include <sensor/NvidiaSensor.h>
+
+using namespace std;
+
+vector<shared_ptr<Sensor>> GPUSensorsFacade::TemperatureSensors() {
+  return vector<shared_ptr<Sensor>>{make_shared<NvidiaSensor>()};
+}