Handling NRT in Scenario Editor (SE)

Which RoadTypes should be available to be built?
 - Tramways are buildable only by players (not city)
   frosch: trams can also be allowed in SE. they would be buildable like canals, and owned by OWNER_NONE.
 - Some RoadTypes could not meet the requirements for a fair play
   - May allow only a particular vehicle category to travel on them, in SE one could not know it
     frosch: no concern imho. scenario creator has to know this stuff.
   - Future roads with house-unfriendly flag used as town roads will make the city disappear when playing
     frosch: same happens if you remove road. no concern imho.
 - Date-introduced RoadTypes will be always available, like industries
   frosch: yes, like industries
 - Owner none?
   frosch: i believe roads near a town center get OWNER_TOWN, roads further away get OWNER_NONE. this should also be present in the code.

Features which could be useful on SE
 - Convert road tool
   - Works regardless of RoadType compatibility?
     frosch: this is also the case in normal game, isn't it? (any conversion is possible, unless some vehicle is on the tile)