Try using an interface instead

So this replaces the Abstract Registry Format with an interface. As I think that's a better option. It deprecates that class and gives a getFormat and setFormat function in the Registry itself.

It allows for people to add their own extra formats if they want (currently impossible unless you put it in the Joomla namespace because of how the AbstractRegistryFormat::getInstance() function works).

However slight disadvantages do exist namely
1. We now have to call INI directly in the JSON format class (though not sure this is a big issue)
2. There is now one format class set up per Registry instance rather than just overall