Allow importing postcodes with no location

Some rows in the ONSPD that have no location - those where the 12th column is a '9'.  The existing importers for ni and gb postcodes automatically ignore these, but it can be useful to include them for existence checks even if we can't give more geographical information about them.

We implement `location_available_for_row` to return `False` if the quality row is `'9'`, `True` otherwise.  This lets us import rows that have no location if we want to.  To keep the Code-Point Open import behaviour we provide an option `--allow-no-location-postcodes` to turn this on; without this option the importer will not import these rows.

mapit_gb/management/commands/mapit_UK_import_onspd.py

@@ -100,13 +100,23 @@ class Command(Command):
             default=False,
             help='Set if you want to import terminated postcodes'
         ),
+        make_option(
+            '--allow-no-location-postcodes',
+            action='store_true',
+            dest='include-no-location',
+            default=False,
+            help='Set if you want to import postcodes without location info (quality: 9)'
+        ),
     )
 
     def pre_row(self, row, options):
         if row[4] and not options['include-terminated']:
             return False  # Terminated postcode
-        if row[11] == '9':
-            return False  # PO Box etc.
+        if not(self.location_available_for_row(row) or options['include-no-location']):
+            return False  # go no further unless we want codes with no location
         if self.code[0:2] in ('GY', 'JE', 'IM', 'BT'):
             return False  # NI and channel islands handled by other commands
         return True
+
+    def location_available_for_row(self, row):
+        return row[11] != '9'  # PO Box etc.