Add validation to create kerb nodes for pedestrian crossings.

[Bonkles]

Description

While mapping sidewalks and crossings, we should consider adding automagic validations for creating kerb nodes wherever crossing ways meeting sidewalks.

We could also consider a power user feature that would just create the kerb nodes with extreme prejudice. According to chad and Said, there is basically never going to be a sidewalk / crossing way intersection without a kerb node needing to be there.

Ex: This user is in the process of drawing a crossing way and has left it close to the sidewalk, and rapid has generated a lint showing the fact that they should probably be connected.

After connecting the two features, we should at least put up a lint saying that there should probably be a kerb node here: