Change default keyStepIncrements to 5

[kazuhide]

Changed the default keyStepIncrements to 5

• When the keyStepIncrements:leftRight value was 1, the volume slidebar couldn't be increased due to a floating point error (over 28).
• Setting the value to >1 solved the issue. Although the value can be customized on the app UI, I'd like to suggest to change the default value.

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[felix-hoc]

Increasing the step size would essentially change the behavior. Instead, I'd suggest to fix it by either making sure to return only integers from the Player, or looking into using Math.round() instead of floor(). But we'd have to test it to make sure it doesn't behave weirdly.