Item options, in fronts tool & data

Item-level options in the tool and data are now created via configuration, to simplify adding these incrementally. Options are now either of: 
* boolean (with false as the default), eg. `isBoosted`, `imageHide`
* editable strings, eg `headline`, `byline`, `imageSrc`

The options show in the tool like this:
![fronts-tool-2](https://cloud.githubusercontent.com/assets/1147913/4291551/52e2b176-3dc5-11e4-98c7-148844e68c2f.png)

In closed articles, only the selected options show:
![fronts-tool](https://cloud.githubusercontent.com/assets/1147913/4291555/6654d766-3dc5-11e4-9b80-75362bcddb0b.png)