new linter: Extend MissingPermissionsChecker to examine API functions

[atodorov]

As of now this checker only examines function based or class based views skipping every other module which isn't named ".views".

API methods also require permissions but they don't look like views (b/c they aren't), e.g. they don't have a first parameter named request.

For the sake of this linter we can safely assume that API methods are in modules named api.py. They also import from modern_rpc, e.g. from modernrpc.core import rpc_method.