LayerControl: fix visibility on multiple renders

[Conengmo]

Closes #1199

LayerControl has instance attributes that we fill when the render method is called. That means that if render is called multiple times, those attributes are changed multiple times. This leads to bugs.

The desired behavior is that each time render is called, the instance attributes act as if the instance was freshly created. Achieve this by calling the reset method at the beginning of the render method. This way, each time render is called, empty instance attributes are used.