ModelInterface addition to clean up ApiClient::deserialize call

[cpiggott]

I added a ModelInterface to clean up the calls that used unknown variables in the ApiClient::deserialize call for Swagger based models.

This removes "breaking" errors when running a php code-sniffer to check for inconsistencies throughout the code-base.

I was unable to find any tests to run this against, so if you have them on your end and would like to test them, please let me know if you find any issue and I'll be happy to clean them up.