Create a study design page

There is currently no way to add/update/delete Sites, Sex, Visit windows, ... from the frontend. Project and Cohort can be changed on subpages of the config module. 

We should have a dedicated page to do the study configuration part of the install process and the administration of these values.
- Project
- Sites
- Visits
- Visit Windows
- Cohort
- Sex
- PSCID
- others?