Add a class field to hold the lifecycle state of the component and Update componentWillReceiveProps to componentDidUpdate

[jhainaua]

Add _isMounted to handle async requests while CountDown is unmounted.

[kenmistry]

this componentDidUpdate change works! it gets rid of the deprecation warning with componentWillReceiveProps. i am running on react-native 0.60.4

[dsernst]

It's a little difficult to review this PR for its stated goals, because of all the whitespace changes.

Can those be separated out into a different PR?

[jhainaua]

I don't have time to address this today or Tuesday. I'll have time to post a revised PR by Wednesday or Thursday. In the meantime; for anyone else who might be having some trouble locating the changes please see my notes below. Thank you for your patience.

1. Ctrl-f or Cmd-f for the _isMounted variable.
2. Compare the lifecycle methods.

NEW CODE: componentDidMount, componentWillUnmount, componentDidUpdate.

vs.

EXISTING CODE: componentDidMount, componentWillUnmount, componentWillReceiveProps

[talalmajali]

@jhainaua what's the goal of tracking the lifecycle in the _isMounted variable?

[talalmajali]

@jhainaua @kenmistry @dsernst i've upgraded the component to use the component did mount, please upgrade to 2.7.1