Improve the sound wave of recording canvas

[TenghuiZhang]

This is the PR to fix #330

[TenghuiZhang]

This is the old sound wave design:

This is the new alert message when the recording reach the max time limit:

This is the new sound wave design when it is recording:

[hoch]

Yes. The new screenshot looks a lot better than the previous version. Can we increase the width of the volume level meter? (5~7 pixels?)