Notifications Settings: added shortcuts to disable/enable all notification settings.

git-svn-id: http://ios.svn.wordpress.org/trunk@4080 7d847f7c-ffe1-4a24-85be-b788d016d96a
Added a missing call to reloadSections from the previous commit.

git-svn-id: http://ios.svn.wordpress.org/trunk@4081 7d847f7c-ffe1-4a24-85be-b788d016d96a
Keep track of blog change listening so we don't add observers twice

After adding several blogs at once, the app got stuck

* App launch called toggleExtraDebuggingIfNeeded and registered an observer
* First blog added called toggleExtraDebuggingIfNeeded and registered an extra observer
* Second blog added called toggleExtraDebuggingIfNeeded twice (2 observers) and registered 2 extra observers
* ...

So for 7 blogs added, thats 2^7 = 128 calls to toggleExtraDebuggingIfNeeded on `[Blog dataSave]`
And every network call which called `[Blog dataSave]` duplicated that number

refs #1565

git-svn-id: http://ios.svn.wordpress.org/trunk@4082 7d847f7c-ffe1-4a24-85be-b788d016d96a