[LYN-2515] Project Manager Gem List (#642)

* [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
* Added drawing the Added/Get button and the platform icons

Code/Tools/ProjectManager/Source/GemCatalog/GemModel.cpp

@@ -55,7 +55,7 @@ namespace O3DE::ProjectManager
         return modelIndex.data(RoleCreator).toString();
     }
 
-    int GemModel::GetPlatforms(const QModelIndex& modelIndex) const
+    GemInfo::Platforms GemModel::GetPlatforms(const QModelIndex& modelIndex) const
     {
         return static_cast<GemInfo::Platforms>(modelIndex.data(RolePlatforms).toInt());
     }