Automatically update DHT nodeslist

List is now automatically fetched from nodes.tox.chat and placed in the
user config directory. The list is updated once every 30 days, and
will attempt to detect problems and re-fetch the list if necessary.

Also fixed a couple file descriptor leaks and cleaned some things up.

src/name_lookup.h

@@ -29,8 +29,7 @@
  * Returns 0 on success.
  * Returns -1 on failure.
  */
-int name_lookup_init(void);
-void name_lookup_cleanup(void);
+int name_lookup_init(int curl_init_status);
 
 int name_lookup(ToxWindow *self, Tox *m, const char *id_bin, const char *addr, const char *message);