Refresh control now only refreshes when appropriate.
Also set LBFSViewController object as property instead of ivar in LBFSLocalDataHandler due to large amount of interaction between the two (keeps in line with coding style).
Improved image caching (see full notes).
- Removed cachedImages dictionary
+ Added cachedVenuePhotos and cachedCategoryImages
	• These have separate 'lastModified' and 'images' dictionaries
+ Use new dictionary structures to only retrieve new images based on novelty or age
	• Novelty = doesn't exist in dictionary, age = older than 1 week
+ Other misc. refactoring to make the code more readable.