[TimePicker] allow set time to null

[qnub]

When i try to set time picker back to null it raises error getHours undefined in null so now i need to make custom hack:

  resetTime(){
    const emptyTime = new Date();
    emptyTime.setHours(0);
    emptyTime.setMinutes(0);
    emptyTime.setSeconds(0);
    emptyTime.setMilliseconds(0);

    this.refs.time.setState({
      time: emptyTime
    });
    this.refs.time.refs.input.setValue(null);
  }

[oliviertassinari]

I think that in the future, we should remove setTime from the API. I would rather add a controlled property: time (very similar to the uncontrolled one defaultTime) than pursuing changing this API.
@qnub @shaurya947 What do you think?

[shaurya947]

props over methods any day, @oliviertassinari 👍

[qnub]

@oliviertassinari Yeah, it'll be good. Alongside with respect of switches to null/undefined values in this prop 👍

[shaurya947]

@oliviertassinari OK to merge?

[oliviertassinari]

👍

[oliviertassinari]

@qnub Thanks!