This commit introduces support to the LTI module for LTI 2.0.
As well as the initial commit the following changes were made
and then squashed into the single commit for integration:

* Fixed bug in services
  Fixed bug which limited characters allowed in values of template
  variables (e.g. vendor ID) in service endpoints.
  Changed language file to refer to tool registrations rather than
  tool proxies.

* Refactored service classes
  Moved classes relating to services into areas where Moodle will
  autoload them

* Ran code through code checker
  Removed all errors reported by the Code checker module
  excluding third-party OAuth.php file.

* UI improvements
  Mainly when adding an external tool to a course - fields which
  should not be changed for a selected tool are either hidden or
  disabled. Admin settings page now shows the Tool Registration
  name against a tool rather than the launch URL, and the
  registration URL replaces the GUID on the tool r...