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

glabels/ColorButton.cpp

@@ -129,7 +129,7 @@ namespace glabels
 
 
 	void ColorButton::setKeys( const merge::Merge*     merge,
-	                           const model::Variables* variables )
+	                           const model::Variables& variables )
 	{
 		mDialog->setKeys( merge, variables );
 	}