Change default text for blank piece title

Change default text to be less programmer-y and more user friendly.
Update specs to test this change.
Update other pieces management examples to test properly.
Modify delete piece button to be smaller target
Add Version#blurb to show preview of #content
Add Piece #content, #title and #blurb as shortcuts

Add Piece#title as a shortcut to Piece#current_version's title.
Add Piece#content as a shortcut to Piece#current_version's content.
Add Piece#blurb as a shortcut to Piece#current_version's blurb.
Add specs to test these methods.
Redesign Pieces layout

Now Pieces path shows title, edit and delete links as well as the blurb
and last modified time.
Fix #22 - Change Pieces path sorting

Pieces path is now sorted with the piece whose current_version was
most recently updated at the very top.
Add tests for this functionality.