Pointer cleanup (#242)

- Made greater use of smart pointers, eliminating many instances of manual memory management
- Do not use pointers at all for many non-polymorphic classes
- Assorted other code cleanup

model/Category.h

@@ -34,7 +34,9 @@ namespace glabels
 		{
 
 		public:
+			Category() = default;
 			Category( const QString& id, const QString& name );
+			~Category() = default;
 
 			QString id() const;
 			QString name() const;