ppf: add new field proxies_added to be able to rate sites

sqlite3 urls.sqlite "alter table uris add proxies_added INT"
sqlite3 urls.sqlite "update uris set proxies_added=0"

dbs.py

@@ -20,6 +20,7 @@ def create_table_if_not_exists(sqlite, dbname):
 			error INT,
 			stale_count INT,
 			retrievals INT,
+			proxies_added INT,
 			added INT
 			)""")