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/Vendor.h

@@ -33,7 +33,9 @@ namespace glabels
 		class Vendor
 		{
 		public:
+			Vendor() = default;
 			Vendor( const QString &name, const QString &url );
+			~Vendor() = default;
 
 			QString name() const;
 			QString url() const;