vector tiles support

• new vector tiles tutorial
• changed API for vector tiles to ZXY
  server/{tileset-name}/{z}/{x}/{y}.{extension}

code refactoring to

• config.js, settings: server, port, data folder path ...
• server.js, API and url routes
• TileService.js, handling of the tiles

maintenance, updated dependencies to latest

• mbtiles (0.9.0)
• express (4.14.4)