Add ProgressBar component

[ItsJonQ]

Add ProgressBar component

This update adds a new ProgressBar component, complete with README and tests.

Example

<ProgressBar value={50} />

Props

Prop	Type	Description
onChange	function	Callback when component value updates. Returns value as percent.
size	string	Determines the size of the input.
value	number/string	Progress value to visualize in component.

Minor update: The className for the Animate component was renamed from animate to Animate.

Resolves: #25

[coveralls]

Coverage remained the same at 100.0% when pulling 2be214f on add-progress-bar into 1f4f9e7 on master.