add 4 icons. bunker_silo (by mdk, modified, see #josm10723, CC0); farmyard (combined of existing JOSM icons); allotments (https://openclipart.org/people/lescinqailes/lescinqailes_Watering_can.svg, modified, PD); meadow (https://openclipart.org/detail/21212/grass-texture-by-rg1024-21212, modified, PD)

git-svn-id: http://svn.openstreetmap.org/applications/share/map-icons@30793 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4