* Remove default app that writes to Firestore.
This ends up running during unit test execution and that doesn't work on
Travis.
* Remove gRPC death tests
These are expensive because they actually are catching abort().
* Rename Firestore/Example/App/macOS_example to macOS
* Update paths to macOS and names to Firestore_Example_macOS
* Add Firestore_Tests_macOS target
This uses a shared Tests Info.plist. This is important because it
configures NSPrincipalClass
* Teach sync_project about Firestore_Tests_macOS
* Add files to Firestore_Tests_macOS
* Add Firestore_Tests_macOS target to the Podfile
* Add HEADER_SEARCH_PATHS to match iOS
* Force C99/C++11 conformance
* pod install after adding Firestore_Tests_macOS
* Get macOS tests to link
* Add spec test json files to the macOS tests
* Remove development code signing
* Disable app sandboxing to allow GoogleTest death tests to succeed.
Besides adding a new macOS example to the project, this:
* Adds a search for roots.pem in root of main bundle
* Accepts swiftformat 0.37 in `style.sh`
* Extends the travis_wait from the default 20 mins to 45 to allow for building iOS and macOS.
* Add an empty GoogleService-Info.plist to the Firestore project
* Add machinery to be able to use GoogleServices-Info.plist in integration tests.
* Refer to instructions if neither a plist nor testing cert is set up
wu-hui