Fixes#1156Fixes#810Fixes#1228
This PR replaces `osmborder`, which is no longer maintained, with `imposm` mappings and SQL code to generate borders. Key features that were moved into the imposm/SQL layer:
1. Grouping by `osm_id` and aggregating by lowest `admin_level` value so that there's only one copy of ways that are members of multiple relations.
2. Filtering out of point features in boundary relations (typically `admin_centre` and `label` roles).
3. Move disputed boundary detection logic into SQL.
This will increase the database size slightly because of the limits of what imposm can do, as some of the filtering is done in the SQL layer after importing, rather than being done in `osmborder`.
This PR adds state name to national borders (`admin_level=2`)
From zoom level 3 there is an added `adm0_l` and `adm0_r` attribute for national borders.
There is 3 main steps:
1) union border lines from OSM and keep separate LineString between intersects
2) create polygons from step 1), create a point in each state polygon, add to this point a state abbreviation from NaturalEarth Data
3) create a short parallel line on the left and right of a small part of the border in 70m distance, and add information about which state overlap this short line.
Brian Sperlongano