moved response messages to config and changed response object while deleting a POI
moved response messages to config and fixed setupCreateTileSetResponse()
moved response messages to config and changed response while deleting POI category
address CR comment: cached an array element
refactored handleUsedCategories() and changed response message while deleting a POI category
refactored getMapId()
added new utils function changeOptionsIfSearchIsValid() and refactored getTileSetsCollection()
CR change addressed
added default 404 handler, updated JSDocs