Simple helper for finding nodes or normals in a selection.
It will create vertical c_lines at all edge start- and end-positions (nodes).
A small menu pops up, where you can define, how the selections shall be treated.
The height (length) of the construction lines can be defined, too (result: top vertices 'follow' the terrain).
This is sometimes also useful for finding small gaps.
Normals will be also shown as helplines.
