Bump version of gRPC.podspec to 0.11

Make servers and stubs context managers

Technically unnecessary, but for consistency with the other beta releases.

Beta maintenance of Python dependencies

Remove check for no workers

I *believe* this is actually safe, and the assert was errantly
copy-pasted a while back.

Fixes #3022

(1) Move dependency on protobuf from grpcio to grpcio_test. While the
most-commonly-foreseen use case of grpcio makes use of protobuf,
technically protobuf is not strictly needed and there's no actual
in-code relationship between grpcio and protobuf.

(2) Loosen the dependency on protobuf from ==3.0.0a3 to >=3.0.0a3.

(3) Update all references to 0.10.0* to 0.11.0.

(4) Alphabetize the grpcio_test dependencies.

Servers and stubs were context managers in the Alpha API; they may not
need to be in the Beta API but it's easy enough to do, eases migration,
and probably helps some use cases.

For now the stub is given empty __enter__ and __exit__ methods; we can
always come back and implement the actual work of context management in
a later change.

Guard against empty vector

Final beta API cleanup

The gRPC protocol objects

Plumb protocol objects through RPC Framework core

(1) Renamed the "beta" module "implementations" because it hasn't been
monolithic since "interfaces" was factored out of it a few changes
back.

(2) Moved ChannelConnectivity from grpc.beta.beta to
grpc.beta.interfaces since it is constants that don't depend on the
beta implementation.

(3) Moved the Server interface definition from grpc.beta.beta to
grpc.beta.interfaces since it is an interface.

(4) Dropped the "create_" prefix from "create_<...>_channel" functions
to better match the other creation functions throughout the codebase.

Use service account credentials for per RPC test

Update interop tests

Fix a case where :status could be returned to applications

Update debian install instructions

Initial work on protocol objects

Fixing bad_client test.

Fixing lingering bytes clipping issue on socket shutdown.

Fix compilation

Before destroying an endpoint, shut it down properly.

For more information, see comments on
https://msdn.microsoft.com/en-us/library/windows/desktop/ms738547(v=vs.85).aspx

Fixes a couple of tests on Windows

Moar Windows fixes

Fix flow control issues

Try even harder to disable PDB generation

Even if the stream was cancelled, notify of its state change.