Re-enabling non-course modules

They were temporarily disabled in c10aa53a090dc6af1264597dcac4f057907e5efa in order to focus on getting Courses working. Now that the basic infrastructure to support running the plugin without BuddyPress is in place, they can be re-enabled.
De-scoping global post variable because it's no longer used
Setting up mocks stubs for the Roles class

Previously the roles class was modified to avoid errors when BuddyPress isn't active, but a better approach is to leave as much of the core classes unmodified as possible and use the mock class instead. The previous commits that this reverts are e5a84f05080def255ec9cfec3cbe47f46a767d2a and 37d69c6b8897a96020d025ffbbadbfeee5637639.