Secure get_creator implementation

**Description**
Currently we just get the creator-name as-is from the untrusted part. To make it secure, we will have to pass the signed-proproposal to ecc which then will have to verify it and extract the creator info. As this also involves MSP validation and alike which tlcc has to do (see e.g., issue #125), this is probably best done via a RPC to TLCC.