Delegate and UI improvements

[andrei-sadagurschi]

• added color picker delegate for getting notified when the color changes;
• added conversion from extended RGB space to sRGB for iOS 10.0 and above (sometimes the returned colors need to be used in sRGB with red, green and blue values between 0.0 and 1.0);
• fixed compile warnings;
• don't recreate color wheel, brightness view and selected color view each time the color is set from outside;
• added laryer corner radius and border to selected color view;

[andrei-sadagurschi]

Done.