[openrailwaymap] Vacancy detection

Hi, just changed the wiki part for the curved switches and saw another discussable tag system: Would it be better to assign the railway:vacancy_detection tags as well to the tracks? That would have the advantage of not having to micro-map all axle counters to just know how the track is detected clear. The additional mapping of axle counters or insulated rail joints shouldn't be effected by that. Yet another advantage would be easier rendering possibilities. So I propose the following changes: + railway:vacancy_detection = [ no || insulated || counted ] on tracks. No changes on the railway=vacancy_detection tags for point objects. Best regards Björn