Convert Overlay to FunctionComponent and expose ref

[alexpaxton]

Closes #301
Closes #102

Changes

• Convert all overlay components to FunctionComponent wrapped with forwardRef
• Refactor Overlay to use a library called react-spring to handle animations

Checklist

Check all that apply

• Updated documentation to reflect changes
• Added entry to top of Changelog with link to PR (not issue)
• Tests pass
• Peer reviewed and approved
• Signed CLA (if not already signed)

[alexpaxton]

Added this is just for displaying this component by itself within storybook

[alexpaxton]

react-spring did not come with any easing functions out of the box

[mavarius]

Good to go. Are we replacing these with Panel at a later time then?

[alexpaxton]

@mavarius yeah I think I'll make that a separate issue

[alexpaxton]

#332