Improve LTI module

Add simplifyed template.
Update lti integration test.
Add getting oauth credentials from course settings.
Add user id transferring to provider.
Improve documentation of lti module.
Pass user_id and course_id to runtime in cms (dev) and tests.
Merge branch 'valera/lti_module' of github.com:edx/edx-platform into valera/lti_module