City census form

* [x] Boot form
* [x] Put in full list of main datasets (i.e. the ones above "new suggestions below this line") - here's the [list of datasets](https://docs.google.com/a/okfn.org/spreadsheet/ccc?key=0Aon3JiuouxLUdEVHQ0c4RGlRWm9Gak54NGV0UlpfOGc#gid=3)
  * Probably plus description / detail (to help when investigating)
  * Do we want to pull this live from the gdoc for the time being to avoid endless copy and pasting (use https://github.com/Recline/backend.gdocs ...)
* [x] Do incremental reveal on the main questions
* [x] Do some validation - e.g. no submission without putting in a city name at the top

## Open Questions

* Instructions on how to go about this - should probably have a tutorial or similar - perhaps worth asking @juliakloiber or @beatricemartini 
* Should we display summary of results (or at least which city / dataset combos have been done) at the top - cf #34  (tabular summary of city census)
* Should we try restricting cities to a specific list (at the moment we have a general "geo feature" lookup ...)