Fix list_contains (a.k.a. the ~= mapcss operator)

The ~= operator also allows for whitespace around the values.
E.g. [a~=y] matches
- a=y
- a=x;y;z
- a=x; y; z
The latter wasn't working with the original implementation

mapcss/mapcss_lib.py

@@ -210,7 +210,7 @@ def string_contains(subject, string):
 
 def list_contains(subject, string):
     if subject is not None and string is not None:
-        return string in subject and string in subject.split(";")
+        return string in subject and any(map(lambda s: s.strip() == string, subject.split(";")))
 
 def at(asset_lat, asset_lon, lat, lon):
     return asset_lat == lat and asset_lon == lon