Fix some XEP-0060 pub sub messages are malformed.

The formForOptions method in Extensions/XEP-0060/XMPPPubSub.m is creating a proper form options but always wrapping it with an options element. It is quite clear from the calls to this method that the expected result is the <x> element.

There are 5 uses which require the x element to be a child of different elements:
- Node subscription options, <x> should be child of <options>
- Subscription configuration, <x> should be child of <options> as well.
- Node creation options, <x> should be child of <configure>, this was malformed. This line shows that the intention was to put x under configure but the formForOptions method was returning the wrong thing:
NSXMLElement *x = [self formForOptions:options withFromType:XMLNS_PUBSUB_NODE_CONFIG];
- Node configuration options, same as the previous one.
- Publish node options, in this case the <x> element should be under <publish-options>. Again the intention was ok but the formForOptions returned the wrong thing.
NSXMLElement *x = [self formForOptions:options withFromType:XMLNS_PUBSUB_PUBLISH_OPTIONS];