ui: switch to single file mode with snippet maximize

* switch back to snippet view with snippet button in file title bar
* use new title bar widget in single view as well
* restore view mode on undo, store current view mode for every message id (added id to message)
* treat view mode switch as adapt message on undo stack
* fixed crash after snippet expansion
* fixed hatching in file title not shown

src/lib_gui/qt/element/QtCodeArea.cpp

@@ -347,7 +347,7 @@ Id QtCodeArea::getLocationIdOfFirstActiveScopeLocation(Id tokenId) const
 	return 0;
 }
 
-uint QtCodeArea::getActiveLocationCount() const
+size_t QtCodeArea::getActiveLocationCount() const
 {
 	uint count = 0;
 
@@ -359,6 +359,18 @@ uint QtCodeArea::getActiveLocationCount() const
 		}
 	}
 
+	if (!count)
+	{
+		for (const Annotation& annotation : m_annotations)
+		{
+			if (annotation.locationType == LocationType::LOCATION_FULLTEXT_SEARCH ||
+				annotation.locationType == LocationType::LOCATION_ERROR)
+			{
+				count++;
+			}
+		}
+	}
+
 	return count;
 }