Added ids to front blocks.

So http://www.theguardian.com/uk#commentisfree will scroll you down to the Comment is free block.
Added ids to front blocks.

So http://www.theguardian.com/uk#commentisfree will scroll you down to the Comment is free block.
Merge pull request #1531 from guardian/front-block-ids

Front block ids
Merge branch 'master' of github.com:guardian/frontend into right-column