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
That might be a possible solution, @spencerldixon. @adammulligan, we couldn't use resources, as Rails' inflection system makes all our `search_path`'s not work. `searches_path` should be used, but that doesn't feel right to me.