Optimise survey

OK, I'm MUCH happier with the way things are running in dev now. All the latest performance tweaks have been pushed to staging too now. Main enhancements are:

* Speeding up actually viewing surveys through a combination of code refactor and database indexes
* Adding a loading icon when a user clicks on 'Edit questionnaire'
* Fetching metadata from a dataset asynchronously when setting up a new questionnaire
*Improving data kitten, which speeds up the metadata fetching too

If we can bump up to Ruby 2 as well, we should be in a much better place.