MDL-44902: Several additions to External Tool (LTI)

* LTI service related changes:
** Fixing exceptions in OAuth library.
** Added new launch option, Existing window: replaces entire page with the LTI object.
** The LTI tool ID used to perform the launch is now sent with the LTI launch parameters.  This is sent back to Moodle on subsequent requests.
** Added $CFG->mod_lti_forcessl to force SSL on all LTI launches.
** Added new LTI launch parameter: tool_consumer_instance_name.  Default value is site full name, but can be customized with $CFG->mod_lti_institution_name.
** The LTI grade service endpoints now set the affected user to the session.  This was required for event listeners.
** Fix the grade deletion service.  Was deleting the grade item instead of just the grade.
** Send error response when LTI instance does not accept grades and grades are being sent.
** Added a method for writing incoming LTI requests to disk for debugging.  Disabled by default.
* Changes for ltisource plugins:
** Can now to plug into backup/restore.
** Can now have settings.php files.
** Can now hook into the LTI launch and edit parameters.
* Several grade changes:
** Added standard_grading_coursemodule_elements to LTI instance edit form.  This means LTI instances can be configured with a grade.
** No longer assumes that grade is out of 100.
** Replaced modl/lti:grade capability with mod/lti:view.
* JS on mod/lti/view.php for resizing the content object has been converted to YUI3.
* Fixed misspellings in language file.
* Added hooks for log post and view actions.
* Bug fix for lti_get_url_thumbprint() when the URL is missing a schema.