Increase permissiveness of pitch matching for "pitch perfect"

[plastichotsprings]

Combined with the tendency of the pitch detection algorithm to give buggy results, need more permissiveness so that people aren't told that they're not on the pitch as often. Otherwise, users who briefly find their pitch as correctly detected and then immediately move out of the range will have the exercise stopped immediately (along with the message "Nice! 1 second").

another related issue would be to add a feature for users to repeat a level of pitch perfect if there was a mistake in the pitch detection -- rather than forcing users to completely start over. this should not be very difficult to add in.