* Refactor more code to use testutils.WasCalled
* incorporate review comments
* Revert watcher_test.go changes
The file is in config package and the other tests use config_test.
So it is not visible.
* Convert config/watcher_test.go t.Fatal calls into require calls
* Moved wasCalled to a public helper function
Now the testutils package has a new function WasCalled
that can be used by anywhere.
* Move OpenGraph code into its own file
* Move OpenGraph image proxying to app layer
* Move test file code out of api4 package
* MM-11272 Add OpenGraph and image dimension metadata to posts
