Copter Extended Tuning: change "Stabilize Roll (Error to Rate)" label to "Angle Roll (Error to Rate)"

[rmackay9]

I think we should rename "Stabilize Roll (Error to Rate)" to "Angle Roll (Error to Rate)". As it is the "Error" doesn't tell the user which kind of error is converted. "Stabilize" is a flight mode so I'm not sure this label is very helpful.

I think we should discuss this a bit with @lthall and perhaps @Hwurzburg and others on the dev call first.

[rmackay9]

@lthall, @Hwurzburg and @bnsgeyer are all happy with this change.