Design TLCC API

**Description**

This work item summaries the new TLCC API exposed to a chaincode enclave based on the recent design diagrams.

New APIs
- get/validate creator
- can_endorse (not, though, while essential for key distribution, it is non-essential/nice-to-have only call during enclave creation and is need only once we move beyond designed peer, ie., beyond MVP. note in the UML diagrams, `can_endorse` is also used by ercc but that doesn't need involving the trusted ledger _enclave_ and probably can be implemented in ercc based straight on the existing lscc).

Besides that, we also have to establish a proper secure channel between ecc and tlcc with corresponding session handling and secure binding of tlcc mrenclave into ecc, verifiable by ercc. See #14 for that.

**Link to feature or bug**

- Secure get_creator implementation #357
- Chaincode enclave / tlcc binding. #14
- Do TLCC cc2scc calls require reflection in r/w set of transactions? #361

**Link to dependent issues**

- Enclave creation and registration #404