Add xAPI verbs' id instead of using the display name only

[otacke]

A very minor suggestion for improvement, probably beyond what the registry is meant for (give an idea of what can be tracked with xAPI):

For the xapiVerbs values, I suggest to also add the verbs' ids which are International Resource Identifiers. The display names are not unique. Different organizations can use the same verb with different notions/definitions. The id is not only unique, but also not relying on English as the default language used for the verbs' display name.

While for attempted the xAPI profile server in fact only lists
http://adlnet.gov/expapi/verbs/attempted as the id (which is used by H5P core automatically via setActivityStarted), the common completed verb yields several results with different meanings/use cases.

So, instead of using

"xapiVerbs": [
  "attempted"
]

this could be

"xapiVerbs": [
  {
    "display": "attempted",
    "id": "http://adlnet.gov/expapi/verbs/attempted"
  }
]