Major changes to the PM/notification counters

Here's a list of changes:
- Some code has been refactored (no more 2 spaces sh**).
- New API method: N.isLoggedIn(), checks if the PM counter exists.
- The counters are now event-based. Each time a new notification or PM is detected, an event is fired.
- NERDZ is now using these events internally, but they are available for every theme/userscript developer.
- You can subscribe to these events with jQuery using the jQuery(document).on ('eventName', function (event, counter, previousCounter) { }).
Event names:
- nerdz:notification: fired each time a new notification is detected.
- nerdz:pm: fired each time a new PM is detected.
- nerdz_internal:set_counter: an internal event used to manually set the counter to a specified value.
WARNING: since NERDZ is using these events you cannot unsubscribe to them using simply jQuery(document).off ('eventName'), otherwise NERDZ notifications would stop working. You must use jQuery namespaces, please read more at http://api.jquery.com/on/#event-names. NERDZ is using the reserved namespace 'nerdz'. Usage of that namespace is forbidden.
The common users will not notice these changes, unless something goes wrong (it shouldn't). The PMs got the priority over the notifications (so you will always see [pm_count] (notification_count) instead of (notification_count) [pm_count]).
Fix strange global variables left by someone

We all know who someone is in this case
Merge pull request #198 from Robertof/master

Major changes to the PM/notification counters