Don't want to be able to switch views while stories are refreshing in Category View
Fixes:
Landscape mode now showing refresh indicator on first start.

When changing grid / list views and then refreshing stories, refresh controller wasn't updating text.
clearCachedObjectsWithManagedObjectContext:context returns TRUE if successful.
reachabilityWithHostName argument needs to be a hostname and not a url.
all of the cell updating is done by MITNewsiPadCategoryViewController
_storyUpdateInProgress is needed here
needed to clear error message
Merge pull request #149 from MIT-Mobile/3.6/ipad-news-refresh

3.6/ipad news refresh