New Web Service core_reportbuilder_reports_list

The new external classes/exporters are covered by unit tests, to manually test you can do the following:

1. Log in as admin
2. Enable web service
3. Generate, and make note of, token for the admin user
4. Select Reports from the user menu
5. Create a new report
6. Execute the following web service request

   $ curl --silent "<WWROOT>/webservice/rest/server.php?moodlewsrestformat=json" --data "wstoken=<TOKEN>&wsfunction=core_reportbuilder_list_reports" | python -m "json.tool"

7. Confirm the following output:

   {

   "reports": [

   {

   // Report data.

   },

   ],

   "warnings": []

   }

8. Confirm that the "Report data" contains information about the report you created (name, source, modified by, etc)