Available drop areas for DropOverlay can be configured via constructor

now.
Better visualization for edge-drops, always shown entire rect as active
drop area and only show a single drop icon.

AdvancedDockingSystem/include/ads/API.h

@@ -26,13 +26,16 @@ ADS_NAMESPACE_BEGIN
 
 enum DropArea
 {
-	TopDropArea,
-	RightDropArea,
-	BottomDropArea,
-	LeftDropArea,
-	CenterDropArea,
-	InvalidDropArea
+	InvalidDropArea = 0,
+	TopDropArea = 1,
+	RightDropArea = 2,
+	BottomDropArea = 4,
+	LeftDropArea = 8,
+	CenterDropArea = 16,
+
+	AllAreas = TopDropArea | RightDropArea | BottomDropArea | LeftDropArea | CenterDropArea
 };
+Q_DECLARE_FLAGS(DropAreas, DropArea)
 
 class InternalContentData
 {
@@ -50,4 +53,4 @@ QSplitter* findParentSplitter(class QWidget* w);
 QSplitter* findImmediateSplitter(class QWidget* w);
 
 ADS_NAMESPACE_END
-#endif
+#endif