Add more debug information to the error message

[JurriaanK]

Some users end up in this condition. This often happens when my.gravitywp.com cloudflare blocks the users ip because they are on cheap shared hosting where the same ip is blocked for abuse by other people.

But there might be other scenario's.
Requested changes:

• Change the output message to:
  'Please try again later. Reason: %s. See our 'documentation'(https://gravitywp.com/doc/license-activation-issues/) to understand why. If the issue persists, please contact support.'

• Add possible reasons; if the response body has 'Cloudflare' and 'blocked, output 'blocked' as reason. Else 'unknown'.

• Output the response content to the handler_class debug log

• Add additional debug information:
  Please include this information if you contact support:
  (Add some debug information to the error message the user can copy)
  Date Time of the request (UTC)
  Response code
  Current website