Grpc logging

[smacker]

Fix: #47
Fix: #11

Changes:

• -v flag overrides log level to debug (as discussed before)
• remove internal gRPC logging, subscribe to the connection status change event. Dummy analyzer doesn't subscribe to statuses because it's expected to run without a connection to data server for it.
• add custom gRPC logging interceptors for server and client. They log incoming/outcoming requests/responses

Reasoning:

Internal gRPC logging logs quite much useless staff without a possibility to filter it by level or anyhow else. The only useful logs I have noticed are connection change status.

Internal gRPC logging doesn't log calls which are very useful. Existing logrus middleware requires workaround because we use src-d/go-log instead of pure logrus. Another problem it logs only when a request is finished. In my experience, it's very useful to log when request has come too in production. (helps to debug cases when the server received request but never responded because of panic/restart/whatever)
It's also very useful for our SDK, when the changes are big enough you can see that request is actually processing instead of empty logs for a dozen seconds. To solve these problems I have created very simple interceptors based on src-d/go-log.

[carlosms]

👏