drop JSONKit dependency

[cvasilak]

Motivation: The sdk uses the old/deprecated JSONKit dependency. From iOS 5+ and later, the platform provides NSJSONSerialization class to perform JSON parsing. This PR adds a new class FHJSON with categories to existing collection foundation classes which invokes the NSJSONSerialization internally. Care was taken to follow the same convenient method name's used by JSONKit, so the changes to the library level plus user application's code are minimal, e.g simple replacement of #import "JSONKit.h" with #import "FHJSON.h"

Further, since many demos use those convenient methods, have adjusted the Documentation target to generate them as public visible (added appledoc), so we are explicit that they can be used in user's application land. Eg. look at the Category References section in the generated html documentation.

To test:

• Simple open the fh-ios-sdk.xcodeproj and run Product->Tests. The tests should build and run successfully.
• Invoke the build.sh script and once the fwk is build, open each demo in the /demos directory. They should work as expected (Note: that you need to adjust fhconfig.plist with your cloud FH app's id etc).

@wei-lee mind to review?

[wei-lee]

Tested & Reviewed. Excellent job! :+1: