Actualize webhooks v2

[kalnik-a-a]

Webhooks were totaly refactored.

1. Existing implementation has no required fields(id, authorization fields..). Methods like DESCRIBE, UPDATE or DELETE were almost useless as we had no opportunity to get required id value.
2. UPDATE method was fixed and now uses PUT instead of POST.
3. UPDATE and CREATE methods accept different sets of fields so Webhook Class was separated into two.
4. One more toJson() method was added to Base Class to implement proper class inheritance behavior. @yepher , now I understand why you suggested using TransmissionBase type instead of method overload in one of closed issues, but I think that such behavior is more likely a bug than feature. In JSON I was expecting to see only fields of Class that was defined in method arguments and not fields from child Class.