Create page to show a piece's versions

Create a VersionsController.
Add an index action to show all a piece's versions.
Add VersionsController spec.
Fix #5 - Add in view for Versions#index action to view a piece's
versions (most recent first).
Add link to piece in the page's title.
Add last modified string for each version.
Add number to each version for user's convenience.
Add in a Versions Management feature.

Add a button link to view a piece's versions from the piece's show page.
Reuse the button link to see a piece's versions on the pieces index.
Update the Pieces Management feature to test this.
Style links on the pieces path with classes instead of inline styles.

Add classes to pieces links
Remove debug code from footer
Update Guardfile to run mgmt specs on views change
Simplify HTML to show piece's last modified date