Convert to modern Objective-C syntax

[cvasilak]

Motivation: The sdk used old syntax and constructs which were superseded by modern objective-c syntax. After applying Xcode magic to auto-convert to use 'modern collection literas/instancetype/NS_ENUM' have made the following changes:

• refactor to maximize property acccess(if visible on the outside) and proper overload in getters where dynamic properties are computed.
• added @protected access for those instance vars that accessed to the sublclasses so it's explicit.
• remove `get prefixes from methods, naming not much used in obj-c
• unneeded @synthesize constructs
• use the common GCD approach for singleton creation

Note: most of the changes where internal API changes not visible to the outside world

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]

Reviewed. Great work. Good to learn a few new things about modern Objective-C.