Projects (first PR)

This PR introduces:
* The `Project` `ProjectItem` `SavedSearch` models
* The `PolymorphicGroup` module
* The `ProjectsController` controller, showing and creating `Project` instances from `Country`, `Region` and `ProtectedArea` instances
* The `SearchController#create` action, creating `SavedSearch` instances, linked to `Project` instances
Pasting this here as a reminder, because we had some trouble when we tried this as a resource for some reason I can't remember. Might be useful: http://nick-hoffman.blogspot.co.uk/2008/11/rails-resources-as-vs-controller.html