Add grid reference labels along the edges and optional per-cell

[Pezmc]

Read from the existing grid in the site_plan (_main) vector tiles

[russss]

Fixed this in SQL:

create or replace view site.grid_labels as select "column" AS label, ST_Project(ST_Centroid(geom), 40, radians(15)) AS geom from grid where row = '1' union all select "row"::text AS label, ST_Project(ST_Centroid(geom), 40, radians(285)) AS geom from grid where "column" = 'A';