Use class extension for private methods
IPHONE-176: Have the App Delegate instantiate the image cache
IPHONE-176: AppSettingController uses image cache instead of direct access to files
IPHONE-176: Have image cache injected in DefaultViewController, then AppSettingController
IPHONE-176: Have image cache injected in GroupController
IPHONE-176: PaginationController using image cache to get images; injected from GroupController
IPHONE-176: Injecting image cache in different places, will be required be later work
IPHONE-176: Injecting image cache in DefinitionManager, not using it yet though, need to review how to best interface image download with cache
IPHONE-176: Injecting image cache in different places (all *SubController classes), will be required be later work
IPHONE-176: All SubController now getting their images from the image cache
IPHONE-176: Fixed memory issues introduced in last commit