Add tag visualization as cylinders around linear model lines

[sruecker]

Piotr's original sketches show these cylinders that represent by their size the number of tags applied to a particular point in the file.

[sruecker]

I have a jpg to attach to this ticket but I don't know how to attach it. Here is a link:
www.ualberta.ca/~sruecker/Piotr_Plotvis_sketch_linear_with_tag_cylinder.jpg