[C2] Add content type items report

[ywarnier]

In the same idea as the internal admin page admin/files_info, we need a way to know where to find a resource of some type (because sometimes we just want to find an example to show of the use of a test, a forum, a blog, etc).

Create a page that shows the different resource types (from the resource_type table). This should be a dropdown box.

When selecting any of these resource types, the system should show a clickable list of base courses and session courses that contain one or more item of this resource type. When clicking any of these, the system sends us directly to the base course or session course's homepage. We don't need (for now) to get directly inside the corresponding course tool. Just to know that this course contains that type of resource.

Load the list only when the user selects a resource type, to avoid loading too much content at once.