Feature request: add UUID's to all features

[codebot]

Currently, we're using the vertex indices to specify the endpoints of most edges (walls, lanes, doors, etc.). As we gradually migrate towards GeoJSON, it would be better to generate UUID's for all vertices and store those UUID's in the edges, to avoid having to maintain the vertex index because those change (for example, if a lower-indexed vertex is deleted).

We're already doing this for alignment-features and alignment-constraints; this ticket is to migrate that idea throughout the rest of the code, especially the vertex objects.