Add tool proxy support to enrol_lti

Get moodle provider to the point where you can give a proxy url and add it to a moodle consumer (and LTI test consumer) and launch it

Outstanding:

• Update LTI library
• Add library to thirdpartylibs.xml
• Make a language string instead of hardcoded “Successful+registration"
• Ensure we can host two different activities/courses and give separate access. (make sure there is no way to launch one tool using another tool’s proxy) Nope, the same credentials from a proxy work with a different launch/base url
• Improve registration page template.
• Remove all todos
• Fix "Invalid or missing lti_message_type parameter" This is caused by the initial curl call moodle consumer does to detect whether something is a cartridge
• Add a check to tool.php to ensure only launch requests can get processed
• Use a separate token for proxies and cartridges. Shouldn't be able to use a proxy if you have the cartridge.
• When you view the proxy directly, it shows the error twice.
• Only display successful registration if it actually was a success
• Fix coding style errors
• Run grunt no js changes? why did CIbot complain...

Split into issues:

• Figure out a way to verify that the correct launch path is being accessed in the tool_proxy onLaunch. We need a way to match consumers to tools (e.g. a new field in the consumer db)
• Look into combining tool.php and proxy.php