feat(Progress): Allow passing in custom style object

[DSBalaban]

Allows for more flexibility in styling

• Bug fix
• New feature
• Chore
• Breaking change
• There is an open issue which this change addresses
• I have read the CONTRIBUTING document.
• My commits follow the Git Commit Guidelines
• My code follows the code style of this project.
• My change requires a change to the documentation.
• • I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

Ran into a scenario where I could use passing in styles in this manner.
My use case involves mapping over a collection and creating slightly rounded progress bars which overlap (to cover the space created at the corners by border-radius), and I could use the ability of passing in zIndex values programmatically.

I realize this makes Progress "special", seeing as none of the other components accept the style prop. If you want me to do this for all components, let me know.

EDIT: DropdownMenu › should not render multiple children when isOpen is false fails, but it shouldn't be because of this PR.

[kyletsang]

Unfortunately, this broke the ability to set style into the parent progress container. Going to expose this feature under a new prop called barStyle.