Fix Timebar for React 17.x

[marklawlor]

Proposed Change:

As per https://reactjs.org/blog/2018/03/27/update-on-async-rendering.html componentWillMount was removed in React 17.

Moved to logic to the constructor as per migration instructions.

Change type

Put an x in the boxes that apply

• [x] Bugfix
• [ ] New feature

Checklist

• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)