add a new button can clear the state of recorder.
[need test]add the button into main AirInstrument

1. if there is empty null exception, please slap me heavily when you met
me next time.
2. please help to test it. if this button is too hard to touch, or too
easy to touch, you can switch the position.
try to hide this button when nothing is recorded.

Please help me to test if it works.