Add curves and levels editing in iPad version

Please allow curves and levels adjustments in the iPad version. These are really very basic features. Moreover, I suspect that not including them is only a business decision, because when I change these settings with an imported style, they are properly applied and later exported via Cloud Transfer. If you're worried about the iPad version competing with the desktop one, just unlock certain features only for users who already own a Pro desktop version. Simple and fair solution. Currently the functionality is so limited that it's really hard to justify the subscription fee.