ui: implemented gui abstraction and dummy view

- added abstract class tree for gui elements.
- implemented concrete gui classes that wrap the qt specific content.
- implemented first DummyView which plays nice with the ViewManager.

review id = 12

src/lib/gui/WidgetWrapper.cpp

@@ -0,0 +1,9 @@
+#include "gui/WidgetWrapper.h"
+
+WidgetWrapper::WidgetWrapper()
+{
+}
+
+WidgetWrapper::~WidgetWrapper()
+{
+}