A first cut of a reworked spreadsheet builder, which plays nice with PMD2.

Squashed commit of the following:

commit 430f9fd450efe61853beae8c2488cb7acc1fe77a
Author: Asa Calow <asacalow@gmail.com>
Date:   Fri Aug 22 14:43:05 2014 +0100

    Passing feature specs.

commit 7a1256bc4a91dd530515369116579401a177d5b2
Author: Asa Calow <asacalow@gmail.com>
Date:   Fri Aug 22 11:40:03 2014 +0100

    Combined preview, edit & show into a single view; "Add data" now in-page rather than in a modal.

commit d4a71d14f460cb5bf0c2f8f751139015364fffcf
Author: Asa Calow <asacalow@gmail.com>
Date:   Thu Aug 21 11:51:00 2014 +0100

    Reworked 'new spreadsheet builder' form.

commit d8dd7cd4c54a4ad87edd85407c40a578f8a93589
Author: Asa Calow <asacalow@gmail.com>
Date:   Thu Aug 21 11:50:19 2014 +0100

    All specs (except the feature specs) now pass.

commit 9871c2cdd7b2d939911365006b4eef20733c7b4a
Author: Asa Calow <asacalow@gmail.com>
Date:   Tue Aug 19 17:50:17 2014 +0100

    WIP