Recording response errors

[SamuelWei]

Fixes #180

• Add isNotFound() to PublishRecordingsResponse, UpdateRecordingsResponse and DeleteRecordingsResponse
• Deprecated isInvalidId() in DeleteRecordingsResponse
• Add isNoRecordings(), isInvalidLang(), isInvalidKind() in PutRecordingTextTrackResponse (see https://docs.bigbluebutton.org/development/api/#putrecordingtexttrack)
• Change the behaviour of json responses to non-existent json keys by no longer throwing exceptions but returning an empty string instead (same as the xml responses)

[SamuelWei]

Should be part of 5.x due to the deprecation