Replace not-fully-initializing DTO constructors

There were some constructors in the DTOs which allowed construction of
DTO which weren't fully initialized. These constructors have been made
private, as they are still used in the 'fromJson' methods. Additionally,
a constructor with all required parameters to fully initialize the
class has been added.

Additionally, the Loader class has been modified, since it no longer can
assume it is able to default construct the parameter type. The parameter
is now stored as an optional.

Closes #15

core/include/JellyfinQt/dto/itemcounts.h

@@ -46,7 +46,21 @@ namespace DTO {
 
 class ItemCounts {
 public:
-	ItemCounts();
+	ItemCounts(	
+		qint32 movieCount,			
+		qint32 seriesCount,			
+		qint32 episodeCount,			
+		qint32 artistCount,			
+		qint32 programCount,			
+		qint32 trailerCount,			
+		qint32 songCount,			
+		qint32 albumCount,			
+		qint32 musicVideoCount,			
+		qint32 boxSetCount,			
+		qint32 bookCount,			
+		qint32 itemCount		
+	);
+
 	ItemCounts(const ItemCounts &other);
 	
 	/**
@@ -181,8 +195,13 @@ protected:
 	qint32 m_boxSetCount;
 	qint32 m_bookCount;
 	qint32 m_itemCount;
+
+private:
+	// Private constructor which generates an invalid object, for use withing ItemCounts::fromJson();
+	ItemCounts();
 };
 
+
 } // NS DTO
 
 namespace Support {