Made EntityFileParser::MergeEntities return the base entity that was created, and also take an optional parent entity to create it under.

include/Engine/Core/EntityFile.h

@@ -77,7 +77,7 @@ public:
         : m_Handler(handler)
         , m_Reader(reader)
     {
-        // 0 is imaginary world entity
+        // 0 is imaginary base parent
         m_EntityStack.push(0);
         m_StateStack.push(State::Unknown);
     }

include/Engine/Core/EntityFileParser.h

@@ -9,12 +9,13 @@ class EntityFileParser
 public:
     EntityFileParser(const EntityFile* entityFile);
 
-    void MergeEntities(World* world);
+    EntityID MergeEntities(World* world, EntityID baseParent = EntityID_Invalid);
 
 private:
     const EntityFile* m_EntityFile;
     EntityFileHandler m_Handler;
     World* m_World = nullptr;
+    EntityID m_FirstEntity = EntityID_Invalid;
     // Maps EntityIDs local to the file to real IDs in the world after they've been 
     // created in order to resolve parent-child relationships.
     std::map<EntityID, EntityID> m_EntityIDMapper;