Reapply "Add initial feeds for the UK"

This reverts commit f2d0c93.

feeds/uk.json

@@ -0,0 +1,16 @@
+{
+    "maintainers": [
+        {
+            "name": "Jonah Brüchert",
+            "github": "jbruechert"
+        }
+    ],
+    "sources": [
+        {
+            "name": "great-britain",
+            "type": "http",
+            "url": "https://gtfs.pro/files/uran/improved-gtfs-great-britain.zip",
+            "fix": true
+        }
+    ]
+}

src/fetch.py

@@ -127,7 +127,8 @@ def postprocess(self, source: Source, path: Path):
 
         output_file_path = str(outdir.absolute() / path.name)
 
-        command = ["gtfstidy", str(path.absolute()), "--output", output_file_path]
+        command = ["gtfstidy", str(path.absolute()), "--check-null-coords",
+                   "--output", output_file_path]
         if source.fix:
             command.append("--fix")