Add `pointSetClicked` event

[thewtex]

Similar to the imageClicked event, add a pointSetClicked event when a point set is clicked.

This involves:

• Enabling picking on the point set polydata
• Adding the event: https://github.com/Kitware/itk-vtk-viewer/blob/00c5b7cac522bde5c8769977a2599663f3ed6c0b/src/createViewer.js#L509
• Emitting the last picked point set, last picked point index in the point set, and last picked point position starting at: https://github.com/Kitware/itk-vtk-viewer/blob/00c5b7cac522bde5c8769977a2599663f3ed6c0b/src/createViewer.js#L551-L559