Create constants for all of the defined modelNames.

Added deviceModelType to UIDevice category to return whether the device is an iPod, iPhone, iPad.
Prefixed category methods with jmo as per Apple documentation https://developer.apple.com/library/ios/documentation/cocoa/conceptual/ProgrammingWithObjectiveC/CustomizingExistingClasses/CustomizingExistingClasses.html#//apple_ref/doc/uid/TP40011210-CH6-SW4