added OpenStreetMap monochrome rendering

Author: napo

data_sources/osm_monochrome/metadata.ini

@@ -0,0 +1,20 @@
+[general]
+id = osm_monochrome
+type = TMS
+is_contrib = True
+
+[ui]
+group = osm
+alias = Openstreetmap monochrome
+icon =  osm_monochrome_symbol.png
+
+[license]
+name = 
+link = 
+copyright_text =
+copyright_link = 
+terms_of_use = 
+
+[tms]
+url = http://{s}.tiles.wmflabs.org/bw-mapnik/{z}/{x}/{y}.png
+zmax = 20