Do not look in configuration file for annotation values

Updated:

Currently scopes, default_host, and port can be represented in both the proto annotations and the configuration file. Let's make it so that these values can only be represented by the proto annotations to be more strict with our interface. (@landrito)

The generator should be able to generate a working client without any annotations using reasonable default values (i.e. localhost for host, etc.). (@jbolinger)

Previously: We should only use `protoc_options` for very high level options, not for specifying package-level configuration. For package-level values we should only look at the annotations and the configuration file (that was specified in the `protoc_options`).