Github: Fix PHP system notices

- Undefined index: hub_app_access_token in api_uri()
  ==> added isset() check
- Undefined property: stdClass::$id in json_commit_changeset()
  ==> use 'sha' instead of 'id'
Improve display of repository 'Extra Info' field

Instead of a foreach loop and individual call to var_dump() on each
element of the info array, we now call var_dump() on the array itself,
so that the displayed information is more easy to read.