[LYN-2515] Project Manager Gem List Base (#603)

* [LYN-2515] Project Manager Gem List Base

* Added gem model based on a standard item model
* Added list view using the gem model
* Added item delegate for a gem according to the UX design
* Removed th gem catalog ui file and replaced it with code
* Moved the gem catalog files into a sub folder

Code/Tools/ProjectManager/Source/ScreenWidget.h

@@ -30,7 +30,7 @@ namespace O3DE::ProjectManager
         }
 
     protected:
-        virtual void ConnectSlotsAndSignals() = 0;
+        virtual void ConnectSlotsAndSignals() {}
 
         ProjectManagerWindow* m_projectManagerWindow;
     };