srt-style: improved icons

* new icon for ferry terminals (previously it was rendered with the
  bus stop symbol)
* new icon for shelters (previously it was rendered just like hotels),
  image taken from
  merkaartor (map-icons/square.small/recreation/shelter.png)
* use sign icon for information=guidepost
* use smaller info icon for information=board
* use viewpoint icon
MerkaartorPlugin: fixed download area cmdline/URL

Both the cmdline and the download URL were broken for JOSM (wrong
order of lat/lon). This is fixed now.
data update (very minor)