Add base SurveyEditor with draggable questions

- Rename `<SurveyHeader/>` to `<Divider/>`
- Move all components to client/app/components
- Switch to fixed with layout

@somethingkindawierd We have quite a bit of overlap - I left all your stuff in when I rebased, but we should talk and agree on an appraoch
Good name change from `SurveyHeader` to `Divider`