make the path view independent of type of connection

make the path view independent of type of connection
I moved the opengl code for drawing multiple tracks with paths
connecting various elements into GlTracks. This also includes the performance
improvement of only drawing a track once.

Unfortunately I disabled the selection code, as I'm not sure how much
should live at the Qt level and how much should live at the opengl level.

Even more difficult is the problem that a segment can belong to _many_
paths. Which makes my old each path having one pathid not so likely to work--
especially since there's a limit to how many names one can have.

Unfortunately for a large dataset, there's a segfault on closing.