GUI feature to ensure that vertices and edges have full connectivity

[codebot]

Currently it's difficult to tell if edges and vertices have the intended connectivity, because it's possible to add lane edges and vertices that look (in the GUI) like they are connected, until you click+drag the vertices around and notice that they aren't. I think it should be possible to create a function that continually checks to ensure that vertices and edges that "look" (visually) like they are connected are actually connected in underlying graph data structure. If they are not connected, the GUI should render a red circle or something, ideally with a pop-up tooltip, to signify that the lanes are not connected, and navigation between them will not be possible.