plagiarism_turnitin: Move EULA so it is displayed before student submits

Signed-off-by: Tony Butler <tonyjbutler@gmail.com>
plagiarism_turnitin: Add function to check that user has accepted EULA

Signed-off-by: Tony Butler <tonyjbutler@gmail.com>
mod_turnitintooltwo: Check connection to TII before verifying EULA

Signed-off-by: Tony Butler <tonyjbutler@gmail.com>