Merge pull request #17 from derjohng/master

I made some change, please review.
Encapsulate DAAppObject init logic
Consolidate request methods
Use proper endpoint for artist lookup, don't use messy user agent tricks
Factor out duplicate code; pass along default VC titles
Silence warnings
Add -shouldShowIncompatibleApps property and deprecate -loadAllAppsWithArtistId:
Consolidate and improve title update logic
Smoother icon loading animation
Increase icon cache limit & automatically purge on memory warnings
More efficient -[DAAppObject isCompatible] method + comments
One-time compatibility check, also check minimum OS version requirement
DAAppObject properties should be readonly
Remove -iconIsPrerendered property; no longer useful
Cast integers to ints before formatting in NSString
Missing string localizations
Use copy instead of strong for potentially mutable properties
Don't use setters/getters in -init
Add a "block list" to indicate apps that should not be displayed. Closes #18
Add proper number formatting to the user rating counts