Merge master into merge-0.14-into-master

Conflicts:
- gRPC.podspec
  - Only had non-trivial changes in the core file list, which will need to be
    regenerated (in gRPC-Core.podspec).
- src/objective-c/BoringSSL.podspec
  - Had trivial conflicts in the version.
- src/objective-c/examples/RemoteTestClient/RemoteTest.podspec
  - Trivial conflicts in quoting.
- src/objective-c/examples/Sample/Sample.xcodeproj/project.pbxproj and
src/objective-c/examples/SwiftSample/SwiftSample.xcodeproj/project.pbxproj
  - The master version is used, pending testing. The 0.14 version had emoji and
    some unneeded entries.
- src/objective-c/tests/Podfile
  - Added CronetFramework pod, and warning silencing from master.
- templates/gRPC.podspec.template
  - Deleted.
- third_party/protobuf
  - Using master commit, but need to verify if it works for frameworks.