Added [WPAnalytics refreshMetadata].

Calling this method allows each analytics tracker the option to
refresh any metadata they may be collecting about the app. This can be
called in response to events in the app that may change the metadata
such as a login or a logout.
Forcing analytics to refresh metadata on sign in.
Refreshing metadata on account creation.
Refreshing metadata on blog removal/wpcom signout.
Changing cast from intValue to integerValue per @aerych's suggestion.
Merge pull request #2043 from wordpress-mobile/issue/2028-update-number-of-blogs-on-sign-in

Update number_of_blogs super property on sign in.