Add checks from Maps.me subway validators

source code: https://github.com/mapsme/subways

Here is the list of checks. Some may already exists in the default JOSM validator, in PT assistant, etc

- [ ] "Stop area has multiple stations".

- [ ] "Tracks in a stop_area relation"

- [ ] "Only exits for a station, no entrances"

- [ ] "No exits for a station"

- [ ] "Stop position is not a node"

- [ ] "Not a stop or platform in a route relation"

- [ ] "Multiple stops for a station in a route relation"

- [ ] "Cannot find nodes in a railway". Detects broken OSM ways with 0 or 1 node.

- [ ] "Stop is nowhere near the track"

- [ ] "Public transport version is 1".

- [ ] "Ambiguous station in route. Please use stop_position or split interchange stations". This happens if a station object (i.e. a railway=station, not a stop_position) is in a route relation, and this station is included into several stop_areas; or when there are multiple stations of the same transport mode in a stop_area.

- [ ] "Untagged object in a route". Occurs quite often, for example when all tags from a stop_position were transferred to another node but old node is kept in a route relation.

- [ ] "An under construction stop/platform in route". Though it's unclear to me whether under-construction features should be added to routes.

- [ ] "Missing station= on a feature". Requires that railway=station/halt object be tagged with 'station=subway/light_rail/monorail' or have '=yes’. ’train’ mode is silently assumed for railways.

- [ ] " is not connected to a station in route". Occurs when a stop_position/platform is not included in a stop_area or the stop_area is missing a station object.

- [ ] "Route has no stops"

- [ ] "Route has only one stop"

- [ ] "Angle between stops around is too narrow, degrees".
A sharp twist of a route most probably indicates incorrect stops order.

- [x] "Route has different network from master"

- [x] "Incompatible PT mode: route_master has and route has "

- [ ] "Route in two route_masters"

- [ ] "Stop area belongs to multiple interchanges"

- [ ] "An empty route master. Please set construction:route if it is under construction"

- [x] Warnings about different colour/ref of route and route_master

- [ ] Warnings about holes in rails

- [x] "Subway entrance is not a node"

- [ ] "Stop position in a 'platform' role in a route"

- [ ] "Platform in a 'stop' role in a route"

- [ ] "Stop is too far from tracks"

- [ ] "Stop position is not on tracks"

- [ ] "Tracks seem to go in the opposite direction to stops".